PATENT DOCUMENT

Publication Number: US-8634860-B2
Application Number: US-68882410-A
Country: US
Kind Code: B2

Title: Location determination using cached location area codes

Abstract:
Methods, program products, and systems for location determination using cached location area codes are described. A mobile device can store a set of location area codes (LACs) of a cellular communications network on the mobile device. Each LAC can represent a location area of the cellular communications network that encompasses at least a predetermined number of cells. Each LAC can be further associated with an estimated geographic area. The estimated geographic area can be defined as a circle centered at a location and having a radius representing an uncertainty of the location. The mobile device can determine a current LAC of the mobile device based on a wirelessly received signal. The mobile device can determine a current location of the mobile device by performing a lookup in the stored set of LACs using the current LAC.

Claims:
What is claimed is: 
     
       1. A method executed by a mobile device, comprising:
 receiving a set of location area codes (LACs) of a cellular communications network, each LAC in the set being associated with a plurality of cells of the cellular communications network, the LAC further associated with a geographic area, the geographic area including a first circle centered at a location and having a first radius representing an uncertainty of the location; 
 determining a current LAC of the mobile device based on a wirelessly received signal; 
 determining a first estimated location of the mobile device, including performing a lookup in the received set of LACs using the current LAC; 
 providing a representation of the first estimated location for display on the mobile device; 
 determining a second estimated location of the mobile device, comprising:
 receiving identifiers of access points of a wireless communications network and a set of locations associated with the access points; 
 calculating an average geographic location using the set of locations; 
 calculating distances between the average geographic location and locations in the set of locations; 
 excluding at least one location from the set based on a distance between the average geographic location and the at least one location; 
 repeating calculating the average geographic location, calculating the distances, and excluding at least one location until an exit condition is satisfied; and 
 designating the second estimated location of the mobile device using a representation having the average geographic location as a center and at least one calculated distance as a dimension, wherein a size of the representation of the second estimated location is smaller than a size of the representation of the first estimated location; and 
 
 providing for display the representation of the second estimated location replacing the representation of the first estimated location. 
 
     
     
       2. The method of  claim 1 , where each LAC corresponds to a location area, the location area encompassing at least the plurality of cells. 
     
     
       3. The method of  claim 1 , further comprising displaying the representation of the first estimated location of the mobile device on a display device as a first circle centered at the first estimated location and having a first radius representing the uncertainty of the first estimated location. 
     
     
       4. The method of  claim 3 , where providing a representation of the second estimated location for display includes displaying a second circle replacing the first circle, the second circle having a second radius that is less than the first radius. 
     
     
       5. The method of  claim 1 , where the identifiers of the access points include Media Access Control (MAC) addresses of the access points. 
     
     
       6. The method of  claim 1 , where the exit condition is satisfied when a number of repetitions reaches a threshold number. 
     
     
       7. The method of  claim 1 , where the exit condition is satisfied when the radius of the circle reaches below a threshold radius. 
     
     
       8. A system, comprising:
 one or more mobile devices configured to perform operations comprising:
 receiving a set of location area codes (LACs) of a cellular communications network, each LAC in the set being associated with a plurality of cells of the cellular communications network, the LAC further associated with a geographic area, the geographic area including a first circle centered at a location and having a first radius representing an uncertainty of the location; 
 determining a current LAC of the mobile device based on a wirelessly received signal; 
 determining a first estimated location of the mobile device, including performing a lookup in the received set of LACs using the current LAC; 
 
 providing a representation of the first estimated location for display on the mobile device; 
 determining a second estimated location of the mobile device, comprising:
 receiving identifiers of access points of a wireless communications network and a set of locations associated with the access points; 
 calculating an average geographic location using the set of locations; 
 calculating distances between the average geographic location and locations in the set of locations; 
 excluding at least one location from the set based on a distance between the average geographic location and the at least one location; 
 repeating calculating the average geographic location, calculating the distances, and excluding at least one location until an exit condition is satisfied; and 
 designating the second estimated location of the mobile device using a representation having the average geographic location as a center and at least one calculated distance as a dimension, wherein a size of the representation of the second estimated location is smaller than a size of the representation of the first estimated location; and 
 
 providing for display the representation of the second estimated location. 
 
     
     
       9. The system of  claim 8 , where each LAC corresponds to a location area, the location area encompassing at least the plurality of cells. 
     
     
       10. The system of  claim 8 , further comprising displaying the representation of the first estimated location of the mobile device on a display device as a first circle centered at the first estimated location and having a first radius representing the uncertainty of the first estimated location. 
     
     
       11. The system of  claim 8 , where providing a representation of the second estimated displaying the current location further includes displaying a second circle replacing the first circle, the second circle corresponding to an estimated location of the mobile device and having a second radius that is less than the first radius. 
     
     
       12. The system of  claim 8 , where the identifiers of the access points include Media Access Control (MAC) addresses of the access points. 
     
     
       13. The system of  claim 8 , where the exit condition is satisfied when a number of repetitions reaches a threshold number. 
     
     
       14. The system of  claim 8 , where the exit condition is satisfied when the radius of the circle reaches below a threshold radius. 
     
     
       15. A computer program product tangibly stored on a non-transitory storage device, the product operable to cause a mobile device to perform operations comprising:
 receiving a set of location area codes (LACs) of a cellular communications network, each LAC in the set being associated with a plurality of cells of the cellular communications network, the LAC further associated with a geographic area, the geographic area including a first circle centered at a location and having a first radius representing an uncertainty of the location; 
 determining a current LAC of the mobile device based on a wirelessly received signal; 
 determining a first estimated location of the mobile device, including performing a lookup in the received set of LACs using the current LAC;
 providing a representation of the first estimated location for display on the mobile device; 
 determining a second estimated location of the mobile device, comprising:
 receiving identifiers of access points of a wireless communications network and a set of locations associated with the access points; 
 calculating an average geographic location using the set of locations; 
 calculating distances between the average geographic location and locations in the set; 
 excluding at least one location from the set based on a distance between the average geographic location and the at least one location; 
 repeating calculating the average geographic location, calculating the distances, and excluding at least one location until an exit condition is satisfied; and 
 designating the second estimated location of the mobile device using a representation having the average geographic location as a center and at least one calculated distance as a dimension, wherein a size of the representation of the second estimated location is smaller than a size of the representation of the first estimated location; and 
 
 
 providing for display the representation of the second estimated location. 
 
     
     
       16. The product of  claim 15 , where each LAC corresponds to a location area, the location area encompassing at least the plurality of cells. 
     
     
       17. The product of  claim 15 , further comprising displaying the representation of the first estimated location of the mobile device on a display device as a first circle centered at the first estimated location and having a first radius representing the uncertainty of the first estimated location. 
     
     
       18. The product of  claim 17 , where providing a representation of the second estimated for display location further includes displaying a second circle replacing the first circle, the second circle having a second radius that is less than the first radius. 
     
     
       19. The product of  claim 15 , where the identifiers of the access points include Media Access Control (MAC) addresses of the access points. 
     
     
       20. The product of  claim 15 , where the exit condition is satisfied when a number of repetitions reaches a threshold number. 
     
     
       21. The product of  claim 15 , where the exit condition is satisfied when the radius of the circle reaches below a threshold radius.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to geographic location determination. 
     BACKGROUND 
     A cellular communications network can include a radio network made up of a number of fixed-location transceivers, also known as base stations or “cell towers.” Each cell tower can serve a geographic area or a “cell.” Cells of the cellular communications network can be grouped into location areas. For example, in a cellular network based on Global System for Mobile communications (GSM) technology, a location area can correspond to a group of cells sharing a Base Station Controller (BSC). Tens or hundreds of cells can share a single BSC, which can handle allocation of radio channels, receive measurements from mobile devices in the cells, and control handovers from cell to cell. The actual geographic area covered by a cell or a location area can vary, for example, between urban and rural areas, and from one cellular service provider to another. A unique number, or “location area code” (LAC), can be assigned to each location area to identify the location area. 
     Multiple mobile devices (e.g., cellular phones) can connect to each cell tower. If a mobile device is wirelessly connected to a cell tower, the mobile device “knows” the cell tower to which the mobile device is currently connected by an identifier of the cell tower (e.g., a cell identifier). The mobile device can also know a current LAC designating a current location area in which the mobile device is located. If the mobile device moves between cells or location areas, the cell identifier and current LAC can be updated automatically for the mobile device. The mobile device can update the current location area code without having to maintain an active wireless connection to a cell tower. 
     SUMMARY 
     Methods, program products, and systems for location determination using cached location area codes are described. A server computer can receive location information from location-aware mobile devices (e.g., GPS-enabled devices) located in a location area of a cellular communications network. The server computer can also receive from the mobile device the location area code associated with the location area in which the mobile devices are located. The server computer can estimate a coarse geographic location of the location area, as well as a number of cells encompassed by the location area using the received information. The server computer can store the estimated geographic locations associated with sufficiently large location areas (e.g., location areas having more than a certain number of cells). The server computer can provide the stored geographic locations to second mobile devices that are not GPS-enabled for estimating current locations of the second mobile devices. 
     Techniques of location determination using cached location area codes can be implemented to achieve the following advantages. A coarse location can be associated with a location area when the actual geography of the location area is unknown. The coarse location of the location area can be used to estimate a current location of a mobile device when the mobile device is in the location area. The estimate can be carrier-independent. The estimate can provide location information for mobile devices not equipped with GPS features. 
     The cached location area codes and associated coarse locations can have a small memory footprint, and can be stored on mobile devices. A mobile device that can periodically receive LAC updates from the network can quickly determine a coarse estimate of a current geographic location of the mobile devices. The determination calculation can include a simple memory lookup, and therefore can be resource efficient For example, the calculation can also lead to less power consumption, which can help avoid frequent charging of the mobile device battery and therefore enhance a user&#39;s experience using the mobile device. The mobile device can improve the coarse estimate upon request. 
     For GPS-enabled mobile devices, estimating a coarse location using the geographic area associated with a LAC can be advantageous when, for example, GPS signals are weak (e.g., inside buildings). On a GPS-enabled mobile device, the geographic area associated with a LAC can be used to provide an almost instantaneous location estimate of the mobile device. For example, when the mobile device is turned on and before the mobile device determines a location based on the GPS signals, an estimated location based on a location area in which the mobile device is located can be displayed. 
     The coarse location estimate can be improved on an as-needed basis. If a user of the mobile device requires more accurate location than the coarse location associated with a LAC, the mobile device can determine a current location based on available wireless (e.g., WiFi) connections, even if the mobile device is not equipped with GPS features or when GPS signals are weak. 
     The details of one or more implementations of location determination using cached LACs are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of adaptive location determination will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overview of techniques of location determination using cached location area codes. 
         FIG. 2A  illustrates adaptive location determination techniques for associating a coarse location with a LAC. 
         FIGS. 2B-2D  illustrate exemplary stages of using adaptive location determination techniques to associate a coarse location with a LAC. 
         FIG. 2E  illustrates adaptive location determination techniques for associating a coarse location with a LAC in a three dimensional space. 
         FIGS. 3A and 3B  are flowcharts illustrating exemplary processes of location determination using cached location area codes. 
         FIG. 3C  is a block diagram illustrating an exemplary system implementing techniques of location determination using cached location area codes. 
         FIG. 4A  is an overview of techniques of location determination using cached location area codes implemented on mobile devices. 
         FIG. 4B  illustrates techniques of improving accuracy of a location associated with a LAC using locations of wireless access points. 
         FIG. 4C  is a flowchart illustrating an exemplary process of determining an estimated location using cached location area codes, executed on a mobile device. 
         FIG. 4D  is a flow chart illustrating an exemplary process of improving accuracy of a location associated with a LAC using locations of wireless access points. 
         FIG. 4E  is a block diagram illustrating an exemplary system implementing techniques of improving accuracy of a location associated with a LAC using locations of wireless access points 
         FIG. 5  illustrates an exemplary user interface for location determination using cached location area codes. 
         FIG. 6  is a block diagram illustrating an exemplary network architecture for implementing the features and operations described in reference to  FIGS. 1-5 . 
         FIG. 7  is a block diagram illustrating an exemplary device architecture of a mobile device implementing the features and operations described in reference to  FIGS. 1-5 . 
         FIG. 8  is a block diagram of an exemplary system architecture for implementing the features and operations described in reference to  FIGS. 1-5 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Overview of Location Determination Using Cached Location Area Codes 
       FIG. 1  is an overview of techniques of location determination using cached location area codes. For convenience, the techniques will be described in reference to a system that implements the techniques of location determination using cached location area codes. 
     The system can include server computer  100  connected to network  120 . Network  120  can be a data communications network (e.g., a packet switching network) or a hybrid of data and voice network. Through network  120 , server computer  100  can communicate with various devices that are connected to network  120 , including mobile devices  122 ,  124 , and  126 . 
     Mobile devices  122 ,  124 , and  126  can be location-aware mobile devices that can be connected to one or more cellular communications networks. The cellular communications networks can each include one or more location areas. The system can determine a coarse location to be associated with each location area using current locations of mobile devices  122 ,  124 , and  126 . The current locations of mobile devices  122 ,  124 , and  126  can be determined using various technologies implemented on mobile devices  122 ,  124 , and  126 . For example, mobile device  102   a  can determine a current location of mobile device  102   a  using Global Positioning System (GPS) signals received though a GPS receiver that is built in or coupled to mobile device  102   a.    
     Each of mobile devices  122 ,  124 , and  126  can be served by a cell tower of the cellular communication network. For example, mobile devices  122   a - c  can be served by cell towers  108   a - c , respectively; mobile device  104  can be served by cell tower  110 ; and mobile devices  126   a  and  126   b  can be served by cell towers  112   a  and  112   b , respectively. In some implementations, a BSC can determine which mobile device can be served by which tower based on channel availability and geographic locations. 
     Cells  102 ,  104 , and  106  can be grouped into one or more location areas (e.g., based on one or more BSC that control cell towers  122 ,  124 , and  126  of the cells). For example, cells  102   a - c  can be grouped into a first location area; cell  104  can belong to a second location area that includes a single cell; and cells  106   a  and  106   b  can be grouped into a third location area. Each cellular service provider can define location areas specific to the service provider. For example, some location areas can be groups of one or two cells, while some location areas can include hundreds of cells. Each cell can cover a geographic area that can be, for example, several square kilometers. A location area can encompass a geographic area that is covered by the cells in the location area. 
     Each location area of the cellular communications network can be associated with a location area code (LAC). The LAC can uniquely identify the location area. The LAC can be a string or a numeric value. For example, in a Public Land Mobile Network, a LAC can have a value range from 0 to 65,535. Location update procedure can allow a mobile device (e.g., mobile device  122   a ) to inform the cellular communications network when mobile device  122   a  moves from one location area (e.g., the first location area that includes cells  102   a - c ) to another (e.g., the second location area that includes cell  104 ). In some implementations, a mobile device can be responsible for detecting and maintaining location area codes of the location where the mobile device is currently located. For example, when mobile device  102   a  finds that a current LAC is different from LAC of last update, device  102   a  can perform another update by sending to the network a location update request. In some implementations, when mobile device  102   a  moves from one location area to a next while not on a call, a random location update can be performed. The random location update can also occur when signal fades. 
     Each cell tower (e.g., cell tower  108   a ) can have a unique identifier (cell ID) associated with the cell tower. A mobile device (e.g., mobile device  122   a ) located within a cell (e.g., cell  102   a ) can acquire the cell ID of the cell tower (e.g., cell tower  108   a ) that serves the cell. For example, when mobile device  122   a  initiates a data or voice communication through cell tower  108   a , mobile device  122   a  can identify the cell ID of cell tower  108   a.    
     A program running on mobile device  102   a  can acquire the current LAC and cell ID for mobile device  102   a . The program can cause mobile device  102   a  to transmit the current LAC, the current cell ID, and the current location of mobile device  102   a  to server computer  100  through network  120 . The program can be configured such that the transmissions occur at a certain time (e.g., when a user finishes a phone conversation and “hangs up” mobile device  102   a , or when the user terminates a data communication session). 
     In some implementations, the transmissions from mobile devices  122 ,  124 , and  126  to server computer  100  can be received through the cell towers. For example, mobile device  126   a  can transmit the current LAC of mobile device  126   a , current cell ID (e.g., cell ID of cell  106   a ), and current location of mobile device  126   a  to server computer  100  through cell tower  112   a  and network  120 . Cell tower  112   a  can be connected to network  120  though one or more gateways. In some implementations, the transmissions from mobile devices  122  to server computer  100  can occur through wireless access points  114   a  and  114   b  of a wireless communications network, which can be distinct from the cellular communications network. An exemplary wireless communications network can be a Wireless Local Area Network (WLAN). For example, mobile devices  122   a - 122   c  can store locations associated with the current LAC and current cell IDs in a cache memory device, and transmit the stored locations, LAC, and cell IDs to server computer  100  when access points  114   a  or  114   b  become available to mobile devices  122   a - 122   c.    
     Upon receiving the information (including LACs, cell IDs, and location coordinates) from mobile devices  122 ,  124 , and  126 , server computer  100  can store the information in a temporary database. After a time period (e.g., a day, or a week) where a statistically significant amount of data has been received, server computer  100  can select from the temporary database certain LACs whose location areas each includes a large enough number of cells. The selected LACs can be used in further computation. The number of cells in each location area can be calculated using a number of distinct cell IDs associated with a single LAC in the received information. Server computer  100  can select those LACs that are associated with a number of distinct cell IDs when the number reaches a threshold (e.g., 30). 
     For each selected LAC, server computer  100  can calculate an estimated geographic area to be associated with the LAC based on the locations received from mobile devices  122 ,  124 , and  126 . In this specification, the term “LAC location” will be used to refer to the estimated geographic area to be associated with a LAC. The LAC location can be a coarse location that corresponds to the location area represented by the LAC. The coarse location can be represented as a circle, whose center can be defined by a latitude and a longitude, and whose radius can correspond to an uncertainty radius. The uncertainty radius can represent a probability that a certain percentage of mobile devices (e.g., 95 percent) are located within the radius. The LAC location associated with a particular LAC does not necessarily match the geographic shape or location of the location area identified by the particular LAC. The LACs and corresponding LAC locations can be stored as location records  118  in LAC location database  116 . 
     For example, location records  118  can include three exemplary LACs. “LAC 1 ” can represent a location area that includes three cells (cells  102   a - c ). “LAC 2 ” can represent a location area that includes one cell (cell  104 ). “LAC 3 ” can represent a location area that includes two cells (cells  106   a - b ). When the threshold for selecting location areas is set (e.g., set to two), coarse locations can be calculated for LACs that are associated with two or more cells. Therefore, in a two-cell threshold scenario, the locations for “LAC 1 ” and “LAC 3 ” can be calculated, whereas the location for “LAC 2 ” can be excluded from the calculation. The latitudes, longitudes, and uncertainty radius of “LAC 1 ” and “LAC 3 ” can be included in records  118 . 
     Server computer  100  can send records  118  to one or more mobile devices (e.g., mobile device  126   b ). In some implementations, records  118  can be programmed into mobile device  126   b  when mobile device  126   b  is shipped to a user (e.g., a cellular service subscriber). Programming records  118  into mobile device  126   b  can occur when mobile device  126   b  leaves a manufacturer. Programming records  118  into mobile device  126   b  can also occur when mobile device  126   b  is initialized (e.g., at a retail store when mobile device  126   b  is purchased). Programming records  118  into mobile device  126   b  can also occur dynamically (e.g., when the subscriber downloads an application program into mobile device  126   b ). Records  118 , once stored on mobile device  126   b , can be updated periodically, upon request, or when necessary, using various wireless or wired, pull or push, automatic or manual updating technologies through network  120  and cell tower  112   b . Records  118 , stored on mobile device  126   b , can be used to estimate a coarse current location of mobile device  126   b  when mobile device  126   b  knows a current LAC. 
       FIG. 2A  illustrates adaptive location determination techniques for associating a coarse location with a LAC. For convenience, the techniques will be described in reference to a system that implements the techniques of locating cells of a cellular communications network using mobile devices. 
     A cellular communications network can be a radio network that includes a number of cells. A cell can be an area served by one or more cell towers. In  FIGS. 2A-2E , cell  202  is served by cell tower  200 . Mobile devices  208  located within the cell can communicate with each other or with other devices (e.g., data servers or landline phones) inside or outside cell  202  through cell tower  200  that serves the cell. Cell  202  can be an area defined by one or more geographic boundaries that are determined by, for example, communication ranges of cell tower  200  and cell towers in neighboring cells. Mobile devices  208  can enter cell  202  when, for example, mobile device  208  switches cell towers to which mobile device  208  was connected to cell tower  200 . 
     Each of mobile devices  208  and other mobile devices represented in  FIGS. 1-3  as a black triangle can be a location-aware device that can determine a current location using various technologies (e.g., GPS). Mobile device  110 , which is represented as a white triangle, can be a non-GPS-enabled mobile device that is not equipped with hardware components that allow the mobile device to determine its current geographic location. X and Y axes of  FIG. 1  are shown to illustrate that locations of mobile devices  208  can be determined on a two-dimensional area defined by axes X and Y. For example, X and Y axes can correspond to longitudes and latitudes, respectively. For convenience, location of cell tower  200  is shown to coincide with point zero on the X and Y axes in  FIG. 1 . In some implementations, an actual location (e.g., latitude and longitude coordinates) of cell tower  200  is optional in the calculations. 
     When mobile devices  208  communicate with cell tower  200 , mobile devices  208  can transmit location information to the system through cell tower  200 . The location information can be associated with a current LAC and an identifier of cell  202  (e.g., cell ID of cell  202 ). The system can use the location information transmitted from multiple mobile devices  208  to determine an estimated geographic area that can be associated with the cell or the LAC. The estimated geographic area does not necessarily enclose a point where cell tower  200  is actually located. Neither is it necessary for the estimated geographic area to correspond to the geometric location or shape of cell  202  or the current location area, although the estimated geographic area can be located within cell  202  and the current location area. The estimated geographic area can correspond to an area where mobile devices (including location-aware devices  208  and non-GPS-enabled device  210 ) are likely to be located when the mobile devices are in cell  202  and the current location area. The estimated geographic area can be used to determine a coarse location of mobile device  210 . 
     The system that has received multiple locations transmitted from mobile device  208  can determine the estimated geographic area using an iterative process (e.g., by performing a multi-pass analysis). In some implementations, the system can initially calculate an average geographic location (e.g., a centroid) using a set that contains locations received from mobile devices  208  that are located in cell  202  that is served by cell tower  200 . In some implementations, the system can use a set that contains locations received from mobile devices  208  that have the same LAC. In each pass of the multi-pass analysis, the system can calculate a new average geographic location based on the locations in the set, calculate a distance between the average geographic location and each location in the set, and exclude from the set one or more outliers. Outliers can be locations in the set that are located the farthest from the average geographic location. The system can repeat the multi-pass analysis until an exit condition is satisfied (e.g., after a certain number of passes have run, or when other exist conditions are satisfied). 
     For example, in various passes of the multi-pass analysis, the estimated geographic area can be circles  203   a ,  204   a , and  206   a , respectively. Centers of circles  203   a ,  204   a , and  206   a  can each correspond to an average geographic location of the locations in the set in a distinct stage (e.g., a pass of the multi-pass analysis). In each pass, the set of locations can be reduced by excluding the outliers. A location can be excluded from the set if the distance between the location and an average geographic location exceeds a threshold. 
     In some implementations, radii of circles  203   a ,  204   a , and  206   a  can each represent an estimated error margin of the geographic areas. The smaller the radius, the more the precision of the estimated geographic location. Each of the radii of a circle  203   a ,  204   a , and  206   a  can be determined based on at least one calculated distance between the average geographic location and each location in the set. The error margin can correspond to a probability that a mobile device&#39;s current location is correctly estimated. 
     The multi-pass analysis can result in a final average geographic location (e.g., center of circle  206   a ) and a final estimated error margin (e.g., radius of circle  206   a ) when the exit condition is satisfied. The final estimated error margin can be defined based on distances (e.g., a longest distance) between the final average geographic location and locations remaining in the set. Circle  206   a  can be associated with cell  202  and used for estimating locations of non-GPS-enabled mobile devices (e.g., mobile device  210 ) connected to cell tower  200 . 
     Once locations of individual cells included in a location area is determined, the LAC location can be similarly calculated by applying the iterative process on the estimated locations of the cells included in the location area. In some implementations, the location representing the LAC can be directly calculated using the locations from mobile devices  208 . 
       FIGS. 2B-2D  illustrate exemplary stages of using adaptive location determination techniques to associate a coarse location with a LAC. For convenience, the techniques will be described in reference to a system that implements the techniques, cell  202  of the cellular communications network and mobile devices  208  as shown in  FIG. 1 . 
       FIG. 2B  illustrates a stage of a multi-pass analysis for calculating an average location. Each black triangle of  FIG. 2B  can represent a mobile device (e.g., mobile device  208 ) located in cell  202 . Each mobile device  208  can be associated with a current location of mobile device  208 . The current location can be represented by geographic coordinates that include a latitude and a longitude of mobile device  208 . 
     Distribution of mobile devices  208  can reflect a snapshot of mobile devices  208  at a particular time (e.g., 8:30 am local time for a time zone in which cell  202  is located) or locations of mobile devices  208  over a period of time (e.g., six hours). In the former case, each mobile device  208  can be associated with a single location. In the latter case, each mobile device  208  can be associated with multiple locations (e.g., when mobile device  208  is moving). Mobile device  208  that is associated with multiple locations can be represented by multiple locations in  FIG. 2B . 
     For example, mobile device  208  can be a location-aware mobile telephone. If a person is using the location-aware mobile telephone while moving (e.g., walking, driving, etc.), the mobile telephone can have a distinct location every minute. In some implementations, the mobile telephone can transmit the location to the system periodically (e.g., every minute) through cell tower  200 . In some implementations, the mobile telephone can cache (e.g., record) the locations periodically (e.g., every minute), and transmit the cached locations when sufficient bandwidths exist such that the transmission does not interfere with performance of the mobile telephone (e.g., when the person finishes talking and hangs up). Each distinct location can be represented as a distinct black triangle in  FIG. 2B . The data transmitted to the system do not need to include privacy information that may be linked to a user of mobile device. For example, a user account name and telephone number need not be transmitted. 
     The system can determine an average geographic location of a set of locations received from mobile devices  208 . The set of locations can include locations received from mobile devices  208  at a particular time or during a particular time period. The average geographic location can be designated as center  233   b  of area encompassed by circle  203   b . Center  233   b  of circle  203   b  need not coincide with the location of cell tower  200 . A distance between the average geographic location and each location in the set can be calculated. Locations whose distances to the center exceed a threshold can be excluded from the set. Circle  203   b  can have radius  234   b  that is calculated based on the longest distance between the average geographic location and locations in a current set. 
       FIG. 2C  illustrates another stage of the multi-pass analysis subsequent to the stage of  FIG. 2B . Locations whose distances to the average geographic location of  FIG. 2B  (center  233   b  of circle  203   b ) exceed a threshold are excluded from the set. The threshold can be configured such that a percentage of locations (e.g., five percent of locations of  FIG. 2B ) are excluded. A new average geographic location can be calculated based on the locations remaining in the set (e.g., the 95 percent of locations remaining). The new average geographic location can be, for example, center  233   c  of circle  204   c . In various implementations, calculating the new average geographic location can include averaging the remaining locations in the set, selecting a medium geographic location in the set (e.g., by selecting a medium latitude or a medium longitude), or applying other algorithms. Algorithms for calculating the average geographic location can be identical in each pass of the multi-pass analysis, or be distinct from each other in each pass. 
     Area encompassed by circle  204   c  can be smaller than the area encompassed by circle  203   b  as determined in a prior pass when outlier locations are excluded. The smaller area can reflect an increased precision of the calculation. Center  233   c  of circle  204   c  does not necessarily coincide with center  233   b  of circle  203   b . In some implementations, radius  234   c  of circle  204   c  can correspond to a remaining location of mobile device  208  that is farthest away from the center  233   c  of circle  204   c . The radius can represent an error margin of the new estimated geographic location calculated in the current pass. 
       FIG. 2D  illustrates an exemplary final stage of the multi-pass analysis. The final pass can produce a final average geographic location that corresponds to a cluster of positions of mobile devices  208 . The final average geographic location can be designated as center  233   d  of circle  206   d . Circle  206   d  can have a radius that corresponds to a final error margin, which is based on a distance between the final average geographic location and a location in the cluster. Circle  206   d  can represent a geographic area in which a mobile device in cell  202  is most likely located based on the multi-pass analysis. 
     Once a geographic area is calculated for each individual cell of a location area, the LAC location of the location area can be calculated based on the individual cells. Calculating the LAC location can include applying the multi-pass algorithm to a set of locations associated with the cells including cell  202 . 
       FIG. 2E  illustrates an exemplary stage of location determination using cached location area codes in a three-dimensional space. Some location-aware mobile devices  208  (e.g., GPS-enabled devices) can identify locations in three-dimensional space. The locations can be represented by latitudes, longitudes, and altitudes. Locating a mobile device in a three-dimensional space can be desirable when an altitude of the mobile device is necessary for locating the mobile device. For example, it can be desirable to determine on which floor the mobile device is located in a high-rise building. 
     In  FIG. 2E , axes X, Y, and Z can be used to indicate a three-dimensional space. For example, axes X, Y, and Z can represent longitude, latitude, and altitude, respectively. For convenience, location of cell tower  200  is shown to coincide with point zero on the X, Y, and Z axes in  FIG. 2E . In some implementations, an actual location (e.g., latitude, longitude, and altitude coordinates) of cell tower  200  is optional in the calculations. 
     Each triangle of  FIG. 2E  can represent a location of a device located in a three-dimensional cell space  222 . The locations can have projections (e.g., projection  232 ) on a plane in the three-dimensional space. The plane can be defined at an arbitrary altitude (e.g., the altitude of cell tower  200 ). Cell space  222  can intersect with the plane at circle  226 . Projection  232  and intersection circle  226  are shown to illustrate the locations of mobile devices  208 . In some implementations, determining the projections and intersections can be optional in the calculations. 
     A multi-pass analysis can associate a geographic space with cell space  222  of a cellular communications network based on a set of locations received from location-aware mobile devices  208  that are located in cell space  222 . In a pass of the multi-path analysis, an average geographic location (e.g., center of space  224 ) can be determined by, for example, averaging the latitudes, longitudes, and altitudes coordinates of locations in the set. Distances between the average geographic location and locations in cell space  222  can be calculated. Locations that are within cell space  222  but are sufficiently far away from the average geographic location can be excluded from the set and from further computations. A radius of sphere  224  can be determined by, for example, the farthest distance between remaining locations in the set and the average geographic location. Circle  230  illustrates projection of the space encompassed by sphere  224  on the plane. 
     The system can repeat the stages of calculating an average geographic location in a set, calculating distances between the average geographic location and the locations in the set, and excluding from the set locations based on the calculated distances. The repetition can continue until an exit condition is satisfied. A space having a center at the average geographic location and a radius that is based on a distance between the average geographic location and a remaining location in the set can be designated as a geographic space that can be associated with the cell space  222 . For convenience, the space enclosed by the sphere having a center at the average geographic location and a radius that is based on a distance between the average geographic location and a remaining location in the set will be referred to as a presence space in this specification. The presence space can indicate a space in which a mobile device (e.g., mobile device  110 ) is likely to be located when the mobile device is in cell space  222  (e.g., when the mobile device is served by cell tower  200 ). 
     Once locations of cells included in a location area is determined, the location representing the LAC can be similarly calculated by applying the iterative process on the estimated locations of the cells included in the location area. In some implementations, the location representing the LAC can be directly calculated using the locations from mobile devices  208 . 
     Exemplary Location Determination Using Cached LAC 
       FIG. 3A  is a flowchart illustrating exemplary process  300  of location determination using cached location area code. Process  300  can be used, for example, to determine a coarse location (e.g., LAC location) associated with a location area of a cellular communications network. The LAC location associated with a location area of a cellular communications network can be used to determine a location of a non-GPS-enabled mobile device. For convenience, process  300  will be described in reference to a system that implements process  300  and location-aware mobile devices  208 . 
     The system can receive ( 302 ), from a first set of mobile devices  208 , the following information: at least one location area code (LAC) of a cellular communications network, the LAC associated with a location area; cell identifiers of the cellular communication network; and a set geographic locations of the first set of mobile devices from one or more mobile devices  208 . Each location can be represented by geographic coordinates (e.g., latitude, longitude, and altitude). In various implementations, the set of locations can correspond to a period of time (e.g., 6 hours, or from 6 am to 10 am of a time zone in which the location area is located). 
     In some implementations, the period of time can be configured to reflect characteristics of specific usage patterns at various hours of a day. An area where mobile devices are most likely located in the location area can vary during the day, indicating various usage patterns in specific hours. For example, the period of time can correspond to “commute time,” “business hours,” “night time,” etc. The characteristics of the time of the day can correspond to various usage patterns of mobile devices  208 . For example, during commute time, mobile devices in the location area can be at or near a freeway; during business hours, the mobile devices in the location area can be at or near an office building; at nighttime, the mobile devices in the location area can spread out without a particular point of concentration. The system can calculate the LAC location based on locations received, for example, from 4 am to 10 am, and recalculate the LAC location based on location received from 10 am to 4 pm, etc. Locations received in each characteristic time period can be grouped into a set in the system. The locations can be stored in any data structure (e.g., set, list, array, data records in a relational database, etc.) on a storage device coupled to the system. 
     The system can calculate ( 304 ) a size to be associated with the LAC. The size to be associated with the LAC can correspond to (e.g., can measure) a number of cells in the location area represented by the LAC. Calculating the size can include examining a number of distinct cell IDs associated with the LAC, based on the information received from mobile devices  208 . 
     The system can select ( 306 ) a LAC based on the calculated size of the LAC. Selecting an LAC can include specifying a size threshold (e.g., 30 cells), and selecting the LAC whose size reaches or exceeds the threshold (e.g., the LACs whose represented location areas include at least 30 cells). In some implementations, selecting a LAC can include ranking the LACs based on the size of the LACs (e.g., the LACs whose represented location areas include the most number of cells can rank the highest) and selecting a number of LACs that are top-ranked (e.g., the top 50,000 LACs). 
     The system can associate ( 308 ) each of the selected LACs with a LAC location. A LAC location may or may not coincide with the actual geographic area of the location area as defined by the cellular service provider. The LAC location may or may not coincide with the cells included in the location area. The actual geographic area of the location area and the cells can be unknown. The LAC location can include a geographic location determined by the set of geographic locations received from mobile devices  208 . The LAC location can be stored on a storage device in association with the LAC. Further details on determining the LAC location will be described below with respect to  FIG. 3B . 
     The system can provide ( 310 ) the selected LAC and the associated LAC location to a second mobile device (e.g., mobile device  210 ) for estimating a current location of the second mobile device. Providing the selected LAC and the associated LAC location to mobile device  210  can include sending the selected LAC and the associated LAC location to mobile device  210  wirelessly. 
       FIG. 3B  is a flowchart illustrating an exemplary process  320  of calculating a LAC location using a set of locations. For convenience, process  320  will be described in reference to a system that implements process  320 . 
     The system can calculate ( 324 ) an average geographic location using the locations in the set of locations received from mobile devices  208 . Calculating the average geographic location can include calculating an average of latitudes, longitudes, and altitudes of the locations in the set, and designating a position at the calculated average latitude, longitude, and altitude as the average geographic location. In some implementations, calculating the average geographic location can include designating a position at a median latitude, median longitude, and median altitude of the positions in the set as the average geographic location. 
     The system can calculate ( 326 ) distances between the locations in the set and the average geographic location. In some implementations, the system can calculate a linear distance between each of the locations in the set and the average geographic location in Euclidean space. In some implementations, the system can calculate a geodesic distance between each of the locations in the set and the average geographic location, taking curvature of the Earth into consideration. 
     The distances calculated in stage  326  can be designated as a radius associated with a center. The center can be the average geographic location calculated in stage  324 , which can be a center of a circle. The radius of the circle can be determined based on at least one distance between a location in the set of locations and the average geographic location. In some implementations, the radius can equal to the longest distance between the average geographic location and a location remaining in the set. In some implementations, the radius can be a distance that, when the circle is drawn using the radius and the average geographic location as a center, the circle can enclose a percentage (e.g., 80 percent) of the locations remaining in the set. The radius can represent a margin of error beyond which an estimation of a location of a non-GPS-enabled mobile device is less likely to be statistically meaningful. 
     The system can exclude ( 328 ) from the set at least one location based on a distance between the average location and the location. In some implementations, the system can exclude locations whose distance to the average geographic location exceeds a threshold distance. In each pass of the multi-pass analysis, the system can increase a precision of the estimated average geographic location by excluding locations that appear to be away from a concentration of locations (e.g., a cluster). A location that is away from a cluster of locations can be less useful in estimating the LAC location associated with the LAC, and can be excluded. In various implementations, the threshold distance can vary from one pass to a next pass. In some implementations, the threshold distance can be a distance to the average geographic location within which a certain percentage (e.g., 95 percent) of locations in the set are located. In some implementations, the threshold distance can be a set of distances corresponding to the passes (e.g., 250 meters for the first pass, 150 meters for the second pass, etc.). The system can exclude at least one location from the set when the distance between the average geographic location and the location exceeds the threshold distance. 
     The system can repeat stages  324 ,  326 , and  328  of process  320  until an exit condition is satisfied. The system can determine ( 330 ) whether an exit condition is satisfied for terminating the repetition. In some implementations, the exit condition can be satisfied when a number of repetitions reach a threshold number (e.g., 10 times). The threshold number, as well as the percentage of locations to exclude, can be configurable to fine tune a balance between certainty (e.g., a larger area in a LAC location can result in more confidence that a mobile device in the LAC is actually located in the location area represented by the LAC) and precision (e.g., a area in a LAC location can result in more accurate location of a mobile device). For example, when the percentage is set to 95 percent and the number of passes is set to 10, the final pass can produce a circle that encompasses about 60 percent of all location data points. 
     In some implementations, the exit condition of stage  330  can be satisfied when the LAC location is sufficiently small. In LACs where mobile devices are highly concentrated, a LAC location can be sufficiently small that further passes will not necessarily increase the precision. The repetition of stages  324 ,  326 , and  328  can terminate when the radius of the circle reaches below a threshold radius. The threshold radius can differ from location area to location area, based on the distribution pattern of the locations in the set received (e.g., number of location data points received, density of the location data points, and concentration areas in the cells). 
     The system can designate ( 332 ) the geographic area as a circle having the average geographic location as a center and a radius based on at least one calculated distance. The geographic area can be associated with a LAC. The center can be represented in latitudes and longitudes. In some implementations where distances are calculated in three-dimensional spaces, the center can further be represented in an altitude. 
       FIG. 3C  is a block diagram illustrating an exemplary system implementing techniques of location determination using cached location area codes. The system can include one or more processors, one or more memory devices storing instructions, and other hardware or software components. The system can include location engine  350  that can be used to determine a LAC location to be associated with a LAC. 
     Location engine  350  can include data collection module  352  that can receive data from various mobile devices through various access points (e.g., access points  114 ) or cell towers (e.g., cell towers  122 ,  124 , and  126 ). The data can include multiple data points that can indicate locations of one or more location-aware mobile devices (e.g., mobile devices  208 ) as well as current LACs and current cell IDs of the mobile devices. In some implementations, the data points can also include information on which time zone mobile devices  208  are located. Data collection module  352  can include data reception module  354 , which can receive data transmitted from mobile devices  208 , and data indexing module  356 . Data indexing module  356  can perform various processing on the received data points. For example, data indexing module  356  can sort latitudes, longitudes, and altitudes based on cell IDs. Data indexing module  356  can also group data into sets based on time periods. For example, a new set of received locations can be created for a configurable period of time (e.g., six hours). 
     Sets of received locations of mobile devices  208 , as well as associating LACs and cell IDs, can be stored in data point database  360 . Data point database  360  can store current and historical locations of various mobile devices  208 . Data point database  360  can include an ad hoc database, relational database, object-oriented database. Data point database  360  can be hosted locally or remotely in relation to location engine  350 . 
     Location calculation module  364  can be utilized to calculate an average geographic location in sets of data points in data points database, calculate distances between the average geographic location and locations of various data points, and exclude locations from the sets for further computation. Location calculation module  364  can perform the calculations for a particular set (e.g., a set of data points associated with a cell ID) until an exit condition is reached for the particular set. Location calculation module  364  can determine LAC locations for each LAC. 
     In some implementations, location calculation module  464  can calculate the sizes of location areas represented by the LACs using LAC size calculator  366 . LAC size calculator  366  can count the number of distinct cell IDs associated with each LAC and determine how many cells are included in each of the location areas. LAC size calculator  366  can exclude those LACs whose sizes are below a threshold (e.g., those LACs having fewer than 30 cells). 
     A LAC location can be defined by a center having the average latitude, longitude, and altitude coordinates of the set of locations. The LAC location can be further defined by a radius determined based on distances from locations in the set of locations to the center. The latitude, longitude, and altitude coordinates of centers for the LAC locations and the radii of the LAC locations can be stored in LAC location database  372 . LAC location database  372  can be updated periodically by location calculation module  364 . 
     The data of LAC location database  372  can be distributed to mobile devices using data distribution module  376 . Data distribution module  376  can send information of LAC locations (e.g., center coordinates and radii) that are associated with LACs to mobile devices (e.g., non-GPS-enabled mobile device  210 ) upon request, through broadcasting, or using various push technology without receiving requests from the mobile devices. 
     Exemplary Process for Determining Locations of Mobile Devices Using Locations of Wireless Access Points 
       FIG. 4A  is an overview of techniques of location determination using cached location area codes performed on mobile devices. Mobile device  400  can be a mobile device that can connect to a cellular communications network through cell towers  401 . Mobile device  400  can receive a current LAC from cell towers  401 . Based on the current LAC, mobile device  400  can determine a current location by performing a lookup of the current LAC in cached LAC location database  404 . The current location can be a coarse location, whose accuracy can be further improved by adaptive location calculations. 
     Mobile device  400  can store, or otherwise be connected to, LAC location database  404 . LAC location database  404  can include a set  405  of location area codes (LACs) of one or more cellular communications networks. Each LAC (e.g., “LAC 1 ”) can be associated with at least a predetermined number of cells of the cellular communications network. The LAC can be associated with a geographic area, the geographic area including a first circle centered at a location and having a first radius representing an uncertainty of the location. The predetermined number of cells can represent a minimum number of cells (e.g., 30) that are required of a LAC to be included in LAC location database  404 . For example, if a location area identified by the LAC “LAC 1 ” includes at least two cells, “LAC 1 ” and “LAC 3 ” can be included in LAC location database  404  in association with the geographic area. The strings “LAC 1 ,” “LAC 2 ,” or “LAC 3 ” are used in this specification for illustrative purposes. An actual LAC can be a hexadecimal value. 
     The geographic area stored in association with a LAC in LAC location database  404  can be an estimate of the location area represented by the LAC. However, the geographic area stored in association with a LAC need not map exactly to the shape, size, or center of the location area represented by the LAC. For example, “LAC 1 ” in LAC location database  404  can represent a location area that includes cells  402   a - c , served by cell towers  401   a - c . The geographic area stored in association with “LAC 1 ” can be a circle, whose center can be inside or outside the polygon formed by cells  402   a - c.    
     Mobile device  400 , when located in a cell (e.g., cell  402   b ) that is included in the location area designated by a LAC (e.g., “LAC 1 ”), can receive the LAC. The LAC representing a location area in which mobile device  400  is located will be referred to as a “current LAC” of mobile device  400 . Mobile  400  can acquire the current LAC according to various protocols of the cellular communication network to which mobile device  400  is connected. For example, the current LAC can be sent from a cell tower (e.g., cell tower  401   b ) to which mobile device  400  is connected. 
     Mobile device  400  can perform a lookup in LAC location database  404  using the LAC received from cell tower  401   b . For example, if the current LAC of mobile device  400  is “LAC 1 ,” mobile device  400  can identify the geographic area (e.g., a circle) that is associated with “LAC 1 ” from LAC location database  404 . 
     Upon identifying the geographic area associated with the current LAC, mobile device  400  can display the geographic area on display device  408 . Display device  408  can include a map display, which can display a stored digital map or a digital map received wirelessly. The geographic area can be displayed as circle  406  overlaying on the map on display device  408 . The center of circle  406  can correspond to the longitude and latitude of the geographic area stored in association with the current LAC. The radius of circle  405  can correspond to a radius of the geographic area, scaled to a display size of the map. 
       FIG. 4B  illustrates techniques of improving accuracy of a location associated with a LAC using locations of wireless access points. Mobile device  410  can be an exemplary mobile device that can use locations of wireless access points to determine its location. An exemplary section of a communication network that includes access points  410  is illustrated. Mobile device  410  can be associated with a current LAC, and can identify a coarse current location based on the current LAC. 
     Mobile device  410  can be wirelessly connected to access point  414   a . Access point  414   a  can be an access point of a WLAN (e.g., a WiFi network). From access point  414   a , mobile device  410  can receive data that include locations of neighboring access points. Mobile device  410  can store the received data on a storage device. The stored data can be updated periodically. 
     In the example shown, mobile device  410  is connected to access point  410   a . In addition, mobile device  410  is within communication ranges to access points  414   b ,  414   c , and  414   d . Mobile devices  410  can identify access points  414   a ,  414   b ,  414   c , and  414   d  under wireless communication protocols used in the WLAN (e.g., IEEE 802.11a). Access points  414   a ,  414   b ,  414   c , and  414   d  can be identified by MAC addresses of the access points or other identifiers (e.g., Bluetooth™ identifiers). 
     Mobile device  410  can identify presence areas  416   a ,  416   b ,  416   c , and  416   d  that are associated with access points  414   a - d , respectively. A “presence area” (e.g., presence area  416   a ) can be an estimated area that is associated with an access point (e.g., access point  414   a ) in which mobile devices connected to access point  414   a  is likely to be located. Identifying presence areas  416   a - d  can include retrieving information on the presence areas  416   a - d  from a memory device coupled to mobile device  410 . In some implementations, mobile device  410  can request from a server the presence areas  416   a - d  by sending to the server identifiers (e.g., media access control (MAC) addresses) of access points  414   a - d.    
     Based on presence areas  416   a - d , mobile device  410  can execute an iterative process (e.g., a multi-pass analysis) on the presence areas  416   a - d . The iterative process can produce geographic area  412 , which can be an estimate of the current geographic location of mobile device  410 . Geographic area  412  can be a geographic space when three-dimensional location information is utilized. Mobile device  410  can display the estimated current location on a display device (e.g., on a map display). The estimated current location can be a location that can improve upon the coarse location determined by using LAC alone. 
       FIG. 4C  is a flowchart illustrating exemplary process  420  of determining an estimated location using cached location area codes, executed on a mobile device. For convenience, process  420  will be described in referenced to mobile device  400  that implements process  420 . 
     Mobile device  400  can receive ( 422 ) a set of location area codes (LACs) of a cellular communications network. Each LAC in the set can be associated with at least a predetermined number of cells of the cellular communications network. The LAC can further be associated with a geographic area (e.g., a LAC location). The geographic area can be defined as a circle, centered at a particular location and having a radius representing an uncertainty of the location. 
     Receiving ( 422 ) the set of LACs can include storing the set of LACs in a read-only memory (ROM) component of mobile device  400 . The ROM component can be installed by a manufacturer. Receiving ( 422 ) the set of LACs can also include downloading the set of LACs from a server computer (e.g., by downloading to mobile device  400  an application program from the server computer upon a request from mobile device  400 ). Receiving ( 422 ) the set of LACs can also include automatically and wirelessly receiving the set of LACs being pushed by the server computer, through a wireless access point or a cell tower. 
     The set of LACs received in stage  422  can be selected based on various criteria. In some implementations, location area size can be a selection criterion. Location area size can correspond to a predetermined number of cells encompassed in the location area. For example, a LAC that corresponds to a location area that encompasses a certain number of cells (e.g., 30 cells) can be included. LACs not satisfying the criterion (e.g., having fewer than a predetermined number of cells) can be excluded. Another selection criterion can be a number of data points received from the LAC. A data point can correspond to a transmission of a location from a location-aware mobile device to the server computer, the location being associated with a LAC. The LAC can be included if the server computer has received a sufficient number of data points (e.g., a statistically significant number such that a LAC location can be calculated). 
     Mobile device  400  can determine ( 424 ) a current LAC of mobile device  400  based on a wirelessly received signal. Determining a current LAC can include querying a processor in mobile device  400  that is dedicated to processing communication functions (e.g., a baseband processor). 
     Mobile device  400  can determine ( 426 ) a current location of mobile device  400 . Determining the current location can include performing a query into LAC location database  404  using the current LAC. The query can retrieve a LAC location, which can be used as a coarse estimate of the current location. The current location can include a circle, for example, that encompasses a city. Performing the coarse estimate can have the advantage of minimizing consumption of resources (e.g., CPU cycles, communication bandwidths, and battery power of mobile device  400 ) in determining a current location. Accuracy of the coarse estimate of the current location can optionally be improved by further calculations. 
     Mobile device can optionally display ( 428 ) the current location of mobile device  400  on a display device. The current location can be displayed as a first circle (e.g., the circle of the LAC location), which can be centered at a location point defined by a latitude and a longitude, and having a radius that can represent an uncertainty of the location point. 
     Displaying ( 428 ) the current location can optionally further include displaying a second circle replacing the first circle. The second circle can correspond to an improved estimate of the current location of mobile device  400 , which can be an improvement upon the coarse estimate based on current LAC. The second circle can have a radius that is less that the radius of the first circle, reflecting the improved accuracy. The second circle can be determined by an adaptive location determination process, which will be described in further detail below with respect to  FIG. 4D . 
       FIG. 4D  is a flowchart illustrating exemplary process  430  of determining a location of a mobile device using locations of wireless access points. For convenience, process  430  will be described in reference to mobile device  410  that implements process  430 . 
     Mobile device  410  can receive ( 432 ) identifiers of access points (e.g., access points  414 ) of a wireless communication network (e.g., a WLAN) and a set of locations associated with the access points. The set of locations can correspond to presence areas  416  or presence spaces associated with the access point. Each location can be represented by geographic coordinates (e.g., latitude, longitude, and altitude). Each location can be associated with an identifier (e.g., a MAC address) of an access point  414 . In various implementations, the set of locations can be received from a server periodically or upon request. 
     Mobile device  410  can calculate ( 434 ) an average geographic location using the locations in the set. Calculating the average geographic location can include calculating an average of latitudes, longitudes, and altitudes of the locations in the set, and designating a position at the calculated average latitude, longitude, and altitude as the average geographic location. In some implementations, calculating the average geographic location can include designating a location at a median latitude, median longitude, and median altitude of the positions in the set as the average geographic location. 
     Mobile device  410  can calculate ( 436 ) distances between the locations in the set and the average geographic location. In some implementations, the system can calculate a linear distance between each of the locations in the set and the average geographic location in Euclidean space. In some implementations, the system can calculate a geodesic distance between each of the locations in the set and the average geographic location, taking curvature of the earth into consideration. 
     The distances calculated in stage  436  can be designated as a radius associated with a center. The center can be the average geographic location calculated in stage  434 , which can be a center of a circle (e.g., circle surrounding geographic area  412 ). The radius of the circle can be determined based on at least one distance between a location in the set of locations and the average geographic location. In some implementations, the radius can equal to the longest distance between the average geographic location and a location remaining in the set. In some implementations, the radius can be a distance that, when a circle is drawn using the radius and the average geographic location as a center, the circle can enclose a percentage (e.g., 80 percent) of the locations remaining in the set. The radius can represent a margin of error beyond which an estimation of a location of a non-GPS-enabled mobile device is less likely to be statistically meaningful. 
     Mobile device  410  can exclude ( 438 ) from the set at least one location based on a distance between the average location and the location. In some implementations, the system can exclude locations whose distance to the average geographic location exceeds a threshold distance. In each pass of the multi-pass analysis, the system can increase a precision of the estimated average geographic location by excluding locations that appear to be away from a concentration of locations (e.g., a cluster). A location that is away from a cluster of locations can be less useful in estimating a current location of mobile device  410 , and can be excluded. In various implementations, the threshold distance can vary from one pass to a next pass. In some implementations, the threshold distance can be a distance to the average geographic location within which a certain percentage (e.g., 95 percent) of locations in the set are located. In some implementations, the threshold distance can be a set of distances corresponding to the passes (e.g., 50 meters for the first pass, 30 meters for the second pass, etc.). The system can exclude at least one location from the set when the distance between the average geographic location and the location exceeds the threshold distance. 
     Mobile device  410  can repeat stages  434 ,  436 , and  438  of process  430  until an exit condition is satisfied. The system can determine ( 440 ) whether an exit condition is satisfied for terminating the repetition. In some implementations, the exit condition can be satisfied when a number of repetitions reach a threshold number (e.g., five times). The threshold number can relate to a number of locations in the originally received set. The threshold number, as well as the percentage of locations to exclude, can be configurable to fine tune a balance between certainty (e.g., a larger presence area can result in more confidence that a mobile device in the cell is actually located in the presence area) and precision (e.g., a smaller presence area can result in more accurate location of a mobile device). For example, when the percentage is set to 95 percent and the number of passes is set to 10, the final pass can produce a circle that encompasses about 60 percent of all location data points. 
     In some implementations, the exit condition of stage  440  can be satisfied when the presence area or presence space is sufficiently small. In areas where access points  414  are highly concentrated, an estimated current location can include an area sufficiently small that further passes will not necessarily increase the precision. The repetition of stages  434 ,  436 , and  438  can terminate when the radius of the circle reaches below a threshold radius. For example, the threshold radius can be 8-10 meters. The threshold radius can be based on radii of presence areas  416 . In some implementations, if some radii of presence areas  416  are sufficiently small, the threshold radius can be small, to reflect a confidence on the estimate. 
     Mobile device  410  can designate ( 442 ) the current location of mobile device  410  using a circle having the average geographic location as a center and a radius based on at least one calculated distance. The center can be represented in latitudes and longitudes. In some implementations, where distances are calculated in three-dimensional spaces, the center can further be represented in an altitude. In some implementations, mobile device  410  can further display the current location on a display device on a map user interface. Exemplary map user interfaces will be described below in reference to  FIG. 5 . 
       FIG. 4E  is a block diagram illustrating an exemplary system implementing techniques of location determination using cached location area code using mobile devices. The system can include one or more processors (e.g., an application processor and a baseband processor), one or more memory devices storing instructions, and other hardware or software components. The system can include location calculator  450  that can be used to determine an improved location estimate for a mobile device (e.g., mobile device  410 ). 
     Location calculator  450  can include LAC location database  452  that can store a set of LACs and corresponding LAC locations. In some implementations, the LACs and corresponding LAC locations stored in LAC location database  452  can be updated periodically or upon request. LAC determination module  454  can determine a current LAC of mobile device  410 . In some implementations, to determine the current LAC of mobile device  410 , LAC determination module  454  can query a baseband processor of mobile device  410  by calling an application programming interface (API) of the baseband processor. In some implementations, LAC determination module  454  can determine a current cell ID in addition to the current LAC. 
     Location query module  456  can perform a query into LAC location database  452  using the current LAC retrieved by LAC determination module  454 . The query can map the current LAC into a LAC location, in accordance to records in LAC location database  452 . The LAC location can be presented to user interface  458  for display. User interface  458  can include a map display, which can display a digital map and overlay the LAC location that has been mapped to the current LAC by location query module  456 . Overlaying the LAC location on the map can include displaying the LAC location as a circle on the map. 
     Location update module  460  can receive from one or more server computers location data on one or more access points of a wireless network. The data can include multiple identifiers of one or more access points (e.g., access points  414 ) as well as locations associated with the access points. In some implementations, the identifiers of the access points can correspond to access points that are located within the LAC location that corresponds to the current LAC of mobile device  410 . Location update module  460  can receive the location data when a user of mobile device  410  requests the data (e.g., when a user requests an improvement of the coarse location estimate based on the LAC). Location update module  460  can also receive the location data automatically. For example, location update module  460  can also receive the location data through an update when mobile device  410  has identified a new current LAC (e.g., by moving from one location area to another location area). In some implementations, the data points received by location update module  460  can include access points that are located within a current cell of mobile device  410 . 
     Location database  462  can store the location data of the access points within the current location area or the current cell. Location database  462  can be updated by location update module  460 , and can be queried by location calculation module  364 . 
     Location calculation module  364  can include access point locator  366 . Access point locator  466  can include devices and software for determining available access points. Available access points can include access points with which mobile device  410  can communicate. Depending on the geographic location of mobile device  410  and the access points, mobile device  410  can be within communication range of multiple access points, even though mobile device  410  may be connected with only one particular access point. Mobile device  410  can use the access points within communication range to perform location calculations to improve upon the coarse location determined based on the current LAC. 
     Location lookup module  468  can query location database  462  and identify a set of locations corresponding to the access points that are within communication range. Location calculation module  464  can calculate an average geographic location in sets of locations identified from location database  462 , calculate distances between the average geographic location and locations of various locations, and exclude locations from the sets for further computation. Location calculation module  464  can perform the calculations for a particular set (e.g., a set of locations identified by location lookup module  468 ) until an exit condition is reached for the particular set. Location calculation module  464  can determine a current location of mobile device  410 . 
     The current location of mobile device  410 , as determined by location calculation module  464 , can be displayed on user interface  458 . The current location can be an improvement of the coarse location determined by location query module  456 . Improving the coarse location can be performed on an as-needed basis. For example, the operations performed by modules  460 ,  462 ,  464 ,  466 , and  468  can occur upon a user request, or when the coarse location is displayed on user interface  458  for a certain amount of time (e.g., 10 seconds), which can indicate that the user may have an interest in acquiring an improved current location. 
     Exemplary User Interfaces of Location Determination Using Cached LAC 
       FIG. 5  illustrates an exemplary user interface for location determination using cached location area code using mobile devices. In  FIG. 5 , example map  502  of a geographic area is displayed on mobile device  500 . Mobile device  500  can be, for example, a handheld computer, a personal digital assistant, a cellular telephone, an electronic tablet, a network appliance, a camera, a smart phone, an enhanced general packet radio service (EGPRS) mobile phone, a network base station, a media player, a navigation device, an email device, a game console, or a combination of any two or more of these data processing devices or other data processing devices. 
     Exemplary map  502  with a geographic area can be displayed on mobile device  500 . Mobile device  500 , when in a location area, can acquire a current LAC. Mobile device  500  can retrieve a LAC location corresponding to the current LAC by requesting from a server LAC location, or query a LAC location database (e.g., LAC location database  452 ) stored on a storage device on mobile device  500 . In some implementations, mobile device  500  can display the map  502  on the touch sensitive display  530  of mobile device  500 . The map  502  can be displayed when a user selects a maps object to view mapping and location based services. In some implementations, objects, such as the maps object, can be selected by voice activation. A search bar  504  and a bookmarks list object  506  can be displayed at the top of the map  502 . Below the bottom of the map one or more display objects can be displayed, for example a search object  508 , a directions object  510 , a map view object  512 , and a current location object  514 . 
     The search bar  504  can be used to find an address or other location on the map. For example, a user can enter their home address in the search bar  504 , and the region containing the address would be displayed on the map  502 . The bookmarks list object  506  can, for example, bring up a Bookmarks list that contains addresses that are frequently visited, such as a user&#39;s home address. The Bookmarks list can also, for example, contain special bookmarks such as the current location (e.g. the current location of mobile device  500 ). 
     Search object  508  can be used to display search bar  504  and other map related search menus. The directions object  510  can, for example, bring up a menu interface that allows the user to enter a start and end location. The interface can then display information (e.g., directions and travel time for a route from the start location to the end location). Map view object  512  can bring up a menu that can allow the user to select display options for map  502 . For example, map  502  can be changed from black and white to color, the background of the map can be changed, or the user can change the brightness of the map. 
     Current location object  514  can allow the user to see geographic area  516  on map  502  indicating where device  500  is currently located. Geographic area  516  can correspond to a LAC location (e.g., circle  206   d ) that can be used as a coarse estimate of the current location of mobile device  500 . The LAC location can have a center that is an average geographic location of data points associated with a location area where mobile device  500  is located. The LAC location can have a radius that can be determined based on a distance between the average geographic location and one or more locations associated with a current location area. The circle surrounding geographic area  516  can be replaced by another circle with smaller radius, when mobile device  500  can improve the accuracy of a current location estimate. A special current location bookmark can be placed in the Bookmarks list when current location object  514  is selected. If the special current location bookmark was previously set in the Bookmarks list, the old bookmark information can, for example, be replaced with the new current location information. In some implementations, the special current location bookmark is tied to the centroid of geographic area  516 . That is, the special current location bookmark can include the coordinates for the centroid of geographic area  516 . Geographic area  516  can be based on location data determined or estimated using location calculator  450  as previously described in reference to  FIG. 4E . Geographic area  516  can, for example, be depicted by a circle, rectangle, square, hexagon, or other enclosed region with crosshairs, or some other distinctive element to differentiate geographic area  516  from map  502 . 
     In some implementations, geographic area  516  can indicate a region in which mobile device  500  is determined or estimated to be located, and the geographic area may not necessarily be centered on the actual current position of mobile device  500 . In this example, mobile device  500  may be located off-center within the geographic area. In another example, geographic area  516  can be centered on an estimated current position of mobile device  500  (e.g., the center of the LAC location). 
     Mobile device  500  can, for example, center the map view on geographic area  516  when the current location object  514  is tapped or otherwise selected. In some implementations, the zoom level of the map can be adjusted based on the accuracy or precision of the location data or the technology, system, or service that provided the location data. For example, the map can be zoomed out when mobile device  500  cannot receive GPS signals for lower accuracy and uses cell tower data to determine its location. The map can be zoomed in for higher accuracy if mobile device  500  is capable of using GPS location data to determine its current location. In some implementations, the zoom level can be based on the velocity of mobile device  500  (e.g., the map can be zoomed out at higher velocities and zoomed in when mobile device  500  is not moving). A combination of accuracy or precision and velocity can also be used. 
     If all methods for retrieving location-based data fail (e.g., when mobile device  500  is not within communication range of any cell tower or wireless access points), and there are no other systems or services available for determining or estimating the current position of mobile device  500 , an error can be displayed to the user and no geographic area is displayed on map  502 . The error can, for example, contain a message to the user informing them of the failure and the possible reason or reasons for the failure. 
     Current location object  514  can be selected, for example, to activate the estimating and displaying of geographic area  516  on map  502 , to get directions to or from the estimated current location (i.e., the centroid of geographic area  516 ), to send the estimated current location of mobile device  500  to a friend (e.g., such that the friend can go to the same location), or to create a bookmark for the estimated current location. 
     Exemplary System Architecture 
       FIG. 6  is a block diagram of an exemplary network operating environment for the mobile devices of  1 - 5 . Mobile devices  602   a  and  602   b  can, for example, communicate over one or more wired and/or wireless networks  610  in data communication. For example, a wireless network  612 , e.g., a cellular network, can communicate with a wide area network (WAN)  614 , such as the Internet, by use of a gateway  616 . Likewise, an access device  618 , such as an 802.11g wireless access device, can provide communication access to the wide area network  614 . 
     In some implementations, both voice and data communications can be established over wireless network  612  and the access device  618 . For example, mobile device  602   a  can place and receive phone calls (e.g., using voice over Internet Protocol (VoIP) protocols), send and receive e-mail messages (e.g., using Post Office Protocol 3 (POP3)), and retrieve electronic documents and/or streams, such as web pages, photographs, and videos, over wireless network  612 , gateway  616 , and wide area network  614  (e.g., using Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP)). Likewise, in some implementations, the mobile device  602   b  can place and receive phone calls, send and receive e-mail messages, and retrieve electronic documents over the access device  618  and the wide area network  614 . In some implementations, mobile device  602   a  or  602   b  can be physically connected to the access device  618  using one or more cables and the access device  618  can be a personal computer. In this configuration, mobile device  602   a  or  602   b  can be referred to as a “tethered” device. 
     Mobile devices  602   a  and  602   b  can also establish communications by other means. For example, wireless device  602   a  can communicate with other wireless devices, e.g., other mobile devices  602   a  or  602   b , cell phones, etc., over the wireless network  612 . Likewise, mobile devices  602   a  and  602   b  can establish peer-to-peer communications  620 , e.g., a personal area network, by use of one or more communication subsystems, such as the Bluetooth™ communication devices. Other communication protocols and topologies can also be implemented. 
     The mobile device  602   a  or  602   b  can, for example, communicate with one or more services  630 ,  640 ,  650 ,  660 , and  670  over the one or more wired and/or wireless networks. For example, one or more location tracking services  630  can calculate LAC locations to be associated with each LAC, determine how many cells are to be associated with each LAC, and create a LAC location database. The LAC location database can be sent to mobile devices  602   a  and  602   b . In some implementations, location tracking services  630  can also calculate locations to be associated with access points. 
     Messaging service  640  can, for example, provide e-mail and/or other messaging services (e.g., Short Message Service (SMS)). Messaging service  640  can allow a current user of a mobile device (e.g., device  602   a ) to communicate with a requester who requests location information of device  602   a . Device security service  650  can, for example, provide functions for analyzing security events to determine security risk factor, sending security commands to mobile devices  602   a  and  602   b , and processing security status information sent from mobile devices  602   a  and  602   b.    
     Location updating service  660  can determine whether to send location information, including LAC location database and locations of one or more access points, to mobile devices  602   a  and  602   b . Upon determination that the information is to be sent (e.g., based on a request from mobile device  602   a  or  602   b ), Location updating service  660  can transmit the information to mobile devices  602   a  and  602   b.    
     Mobile device  602   a  or  602   b  can also access other data and content over the one or more wired and/or wireless networks. For example, content publishers, such as news sites, Rally Simple Syndication (RSS) feeds, web sites, blogs, social networking sites, developer networks, etc., can be accessed by mobile device  602   a  or  602   b . Such access can be provided by invocation of a web browsing function or application (e.g., a browser) in response to a user touching, for example, a Web object. 
     Exemplary Mobile Device Architecture 
       FIG. 7  is a block diagram of an exemplary architecture  700  for the mobile devices of  FIGS. 1-6 . A mobile device can include memory interface  702 , one or more data processors, image processors and/or central processing units  704 , and peripherals interface  706 . Memory interface  702 , one or more processors  704  and/or peripherals interface  706  can be separate components or can be integrated in one or more integrated circuits. The various components in mobile device  208 , for example, can be coupled by one or more communication buses or signal lines. 
     Sensors, devices, and subsystems can be coupled to peripherals interface  706  to facilitate multiple functionalities. For example, motion sensor  710 , light sensor  712 , and proximity sensor  714  can be coupled to peripherals interface  706  to facilitate orientation, lighting, and proximity functions of the mobile device. Location processor  715  (e.g., GPS receiver) can be connected to peripherals interface  706  to provide geopositioning. Electronic magnetometer  716  (e.g., an integrated circuit chip) can also be connected to peripherals interface  706  to provide data that can be used to determine the direction of magnetic North. Thus, electronic magnetometer  716  can be used as an electronic compass. 
     Camera subsystem  720  and an optical sensor  722 , e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as recording photographs and video clips. 
     Communication functions can be facilitated through one or more wireless communication subsystems  724 , which can include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem  724  can depend on the communication network(s) over which a mobile device is intended to operate. For example, a mobile device can include communication subsystems  724  designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi or WiMax network, and a Bluetooth network. In particular, the wireless communication subsystems  724  can include hosting protocols such that the mobile device can be configured as a base station for other wireless devices. 
     Audio subsystem  726  can be coupled to a speaker  728  and a microphone  730  to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording, and telephony functions. 
     I/O subsystem  740  can include touch screen controller  742  and/or other input controller(s)  744 . Touch-screen controller  742  can be coupled to a touch screen  746  or pad. Touch screen  746  and touch screen controller  742  can, for example, detect contact and movement or break thereof using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with touch screen  746 . 
     Other input controller(s)  744  can be coupled to other input/control devices  748 , such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of speaker  728  and/or microphone  730 . 
     In one implementation, a pressing of the button for a first duration may disengage a lock of the touch screen  746 ; and a pressing of the button for a second duration that is longer than the first duration may turn power to mobile device  410  on or off. The user may be able to customize a functionality of one or more of the buttons. The touch screen  746  can, for example, also be used to implement virtual or soft buttons and/or a keyboard. 
     In some implementations, mobile device  410  can present recorded audio and/or video files, such as MP3, AAC, and MPEG files. In some implementations, mobile device  410  can include the functionality of an MP3 player, such as an iPod™ Mobile device  410  may, therefore, include a pin connector that is compatible with the iPod. Other input/output and control devices can also be used. 
     Memory interface  702  can be coupled to memory  750 . Memory  750  can include high-speed random access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, and/or flash memory (e.g., NAND, NOR). Memory  750  can store operating system  752 , such as Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. Operating system  752  may include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, operating system  752  can include a kernel (e.g., UNIX kernel). 
     Memory  750  may also store communication instructions  754  to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers. Memory  750  may include graphical user interface instructions  756  to facilitate graphic user interface processing; sensor processing instructions  758  to facilitate sensor-related processing and functions; phone instructions  760  to facilitate phone-related processes and functions; electronic messaging instructions  762  to facilitate electronic-messaging related processes and functions; web browsing instructions  764  to facilitate web browsing-related processes and functions; media processing instructions  766  to facilitate media processing-related processes and functions; GPS/Navigation instructions  768  to facilitate GPS and navigation-related processes and instructions; camera instructions  770  to facilitate camera-related processes and functions; magnetometer data  772  and calibration instructions  774  to facilitate magnetometer calibration. The memory  750  may also store other software instructions (not shown), such as security instructions, web video instructions to facilitate web video-related processes and functions, and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions  766  are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively. An activation record and International Mobile Equipment Identity (IMEI) or similar hardware identifier can also be stored in memory  750 . Memory  750  can include location instructions  776  that can be used to transmit a current location to an access point, and to determine an estimated current location based on location data associated with access points to which the mobile device is within a communication range. 
     Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. Memory  750  can include additional instructions or fewer instructions. Furthermore, various functions of the mobile device may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits. 
     Exemplary System Architecture 
       FIG. 8  is a block diagram of an exemplary system architecture  800  for implementing the features and operations described in reference to  FIGS. 1-5 . Other architectures are possible, including architectures with more or fewer components. In some implementations, architecture  800  includes one or more processors  802  (e.g., dual-core Intel® Xeon® Processors), one or more output devices  804  (e.g., LCD), one or more network interfaces  806 , one or more input devices  808  (e.g., mouse, keyboard, touch-sensitive display) and one or more computer-readable mediums  812  (e.g., RAM, ROM, SDRAM, hard disk, optical disk, flash memory, etc.). These components can exchange communications and data over one or more communication channels  810  (e.g., buses), which can utilize various hardware and software for facilitating the transfer of data and control signals between components. 
     The term “computer-readable medium” refers to any medium that participates in providing instructions to processor  802  for execution, including without limitation, non-volatile media (e.g., optical or magnetic disks), volatile media (e.g., memory) and transmission media. Transmission media includes, without limitation, coaxial cables, copper wire and fiber optics. 
     Computer-readable medium  812  can further include operating system  814  (e.g., Mac OS® server, Windows® NT server), network communication module  816 , database interface  820 , data collection module  830 , data distribution module  840 , and location calculation module  850 , as described in reference to  FIGS. 1-5 . Operating system  814  can be multi-user, multiprocessing, multitasking, multithreading, real time, etc. Operating system  814  performs basic tasks, including but not limited to: recognizing input from and providing output to devices  806 ,  808 ; keeping track and managing files and directories on computer-readable mediums  812  (e.g., memory or a storage device); controlling peripheral devices; and managing traffic on the one or more communication channels  810 . Network communications module  816  includes various components for establishing and maintaining network connections (e.g., software for implementing communication protocols, such as TCP/IP, HTTP, etc.). Database interface  820  can include interfaces to one or more databases (e.g., LAC location database  116 ) on a file system. The databases can be organized under a hierarchical folder structure, the folders mapping to directories in the file system. Data collection module  830  can include components for collecting data from multiple mobile devices wirelessly connected to system  800 . Data distribution module  840  can perform various functions for transmitting location data (e.g., location records  118 ) in association with LACs of a cellular communications network to various computing devices, including mobile devices. Location calculation module  850  can include one or more components (e.g., location engine  350 ) for performing calculations on locations received from mobile devices. 
     Architecture  800  can be included in any device capable of hosting a database application program. Architecture  800  can be implemented in a parallel processing or peer-to-peer infrastructure or on a single device with one or more processors. Software can include multiple software components or can be a single body of code. 
     The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language (e.g., Objective-C, Java), including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, a browser-based web application, or other unit suitable for use in a computing environment. 
     Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors or cores, of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. 
     The features can be implemented in a computer system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include, e.g., a LAN, a WAN, and the computers and networks forming the Internet. 
     The computer system can include clients and servers. A client and server are generally remote from each other and typically interact through a network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. For example, the location-aware devices are referred to as GPS-enabled. Location-aware mobile devices are not necessarily based on GPS technology. For example, mobile devices that can determine a location using triangulation are location-aware mobile devices and can be used in determining a LAC location. Cells are represented as hexagons in the figures. The actual shape of a cell can vary. Locations are described as “circles.” The term “circle” used in this specification can include any geometric shape (e.g., an ellipsis, a square, a convex or concave polygon, or a free-style shape) that need not be perfectly circular but is closed or has an appearance of an enclosure. The radius of a geometric shape that is not perfectly circular can include an average distance between various points on the boundary of the geometric shape and a center of the geometric shape. Accordingly, other implementations are within the scope of the following claims.

Metadata:
Filing Date: 20100115
Publication Date: 20140121
Grant Date: 20140121
Priority Date: 20100115
Inventors: HUANG RONALD K.
MAYOR ROBERT
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W64/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W64/00", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44277937