Patent Publication Number: US-6904358-B2

Title: System for displaying a map

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a system for displaying a map using a mobile (portable) terminal device. 
   2. Description of the Related Art 
   One of the information providing services offered by cellular telephone companies or affiliated companies is transmitting map data to a cellular phone so that a map is displayed in a display screen of the cellular phone. In general, a data server can include map data to provide map data of various areas. When a user of a cellular phone operates the cellular phone to specify a desired area, information about the specified area is transmitted by wireless communication to a data server from the cellular phone. Then, map data that matches the specified area information is transmitted by wireless communication back to the cellular phone from the data server so that a map of the desired area is displayed in the display screen of the cellular phone. 
   A user of a mobile or portable terminal device such as a cellular phone usually sees a map when the user visits an unfamiliar place. The user often does not know which direction is the north or south. The map is generally displayed in the cellular phone screen with the top of the map being directed to the north. Unless the user knows which direction is the north, the displayed map is difficult to use. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a system for displaying a map in a display screen of a mobile terminal device such that a user of the mobile terminal device can easily understand relationship between a heading (or moving) direction of the user and a direction of the displayed map. 
   According to a first aspect of the present invention, there is provided a system for displaying a map in a display unit of a mobile terminal device, the system comprising a terminal detector for detecting if the mobile terminal device exists in a first region on a path, a transmitter for transmitting map data representing a map of and around the first region to the mobile terminal device when the terminal detector detects that the mobile terminal device exists in the first region, a receiver for receiving the map data from the transmitter, and a controller for causing the display unit to display the map based on the map data received by the receiver such that a top of the map is aligned with a top of the display unit. 
   According to a second aspect of the present invention, there is provided a host device for transmitting map data to a mobile terminal device, comprising a terminal detector for detecting if the mobile terminal device exists in a first region on a path, and a transmitter for transmitting map data representing a map of and around the first region to the mobile terminal device when the terminal detector detects that the mobile terminal device exists in the first region. 
   According to a third another aspect of the present invention, there is provided a method of displaying a map in a display unit of a mobile terminal device, comprising the steps of (A) detecting if the mobile terminal device exists in a first region on a path, (B) transmitting map data representing a map of and around the first region to the mobile terminal device when existence of the mobile terminal device in the first region is detected in Step A, (C) receiving the map data, and (D) causing the display unit to display the map based on the received map data such that a top of the displayed map is aligned with a moving direction of the mobile terminal device. 
   According to a fourth aspect of the present invention, there is provided a system for displaying a map in a display unit of a mobile terminal device, comprising a first terminal detector for detecting if the mobile terminal device exists in a first region on a path, a second terminal detector for detecting if the mobile terminal device exists in a second region other than the first region on the path, a first transmitter for transmitting first map data representing a first map of and around the first region to the mobile terminal device when the first terminal detector detects that the mobile terminal device exists in the first region, a second transmitter for transmitting second map data representing second map of and around the second region to the mobile terminal device when the second terminal detector detects that the mobile terminal device exists in the second region, a receiver for receiving the first map data from the first transmitter and the second map data from the second transmitter, and a controller for causing the display unit to display the first or second map based on the first or second map data received by the receiver such that a top of the displayed first or second map is aligned with a moving direction of the mobile terminal device. 
   According to a fifth aspect of the present invention, there is provided a host device for transmitting map data to a mobile terminal device, comprising a first terminal detector for detecting if the mobile terminal device exists in a first region on a path, a second terminal detector for detecting if the mobile terminal device exists in a second region other than the first region on the path, a first transmitter for transmitting first map data representing a first map of and around the first region to the mobile terminal device when the first terminal detector detects that the mobile terminal device exists in the first region, and a second transmitter for transmitting second map data representing second map of and around the second region to the mobile terminal device when the second terminal detector detects that the mobile terminal device exists in the second region. 
   According to a sixth aspect of the present invention, there is provided a method of displaying a map in a display unit of a mobile terminal device, comprising the steps of (A) detecting if the mobile terminal device exists in a first region on a path, (B) detecting if the mobile terminal device exists in a second region other than the first region on the path, (C) transmitting first map data representing a map of and around the first region to the mobile terminal device when presence of the mobile terminal device in the first region is detected in Step A, (D) transmitting second map data representing a map of and around the second region to the mobile terminal device when presence of the mobile terminal device in the second region is detected in Step B, and (E) receiving at least one of the first and second map data and causing the display unit to display the map based on the received map data such that a top of the displayed map is aligned with a moving direction of the mobile terminal device. 
   According to a seventh aspect of the present invention, there is provided a mobile terminal device comprising a display unit, a receiver for receiving map data, a controller for causing the display unit to display a map based on the map data received by the receiver, and a direction detector for detecting a direction of the mobile terminal device, wherein the controller converts the received map data on the basis of the direction of the mobile terminal device detected by the direction detector such that the map is displayed in a particular direction regardless of the direction of the mobile terminal device. 
   According to an eight aspect of the present invention, there is provided a mobile terminal device comprising a display unit, a receiver for receiving map data, and a controller for causing the display unit to display a map based on the map data received by the receiver, wherein when the receiver receives first map data of a first cell within a predetermined period after receiving second map data of a second cell other than the first cell, the controller ignores the first map data and causes the display unit to keep displaying the map based on the second map data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a block diagram of a map displaying system according to one embodiment of the present invention; 
       FIG. 2  illustrates a map around a ground entrance/exit of a subway together with two cells used by the system shown in  FIG. 1 ; 
       FIG. 3  illustrates a sequence diagram for displaying a map executed by the system shown in  FIG. 1 ; 
       FIG. 4  illustrates a map displayed in a portable terminal device of the system shown in  FIG. 1 ; 
       FIG. 5  illustrates two cells defined at an entrance/exit of a department store when the system shown in  FIG. 1  is designed for a portable terminal device user who enters and exits the department store; 
       FIG. 6  illustrates a block diagram of a map displaying system according to another embodiment of the present invention; 
       FIG. 7  illustrates a sequence diagram for displaying a map executed by the system shown in  FIG. 6 ; 
       FIG. 8  illustrates a block diagram of a map displaying system according to still another embodiment of the present invention; 
       FIG. 9  illustrates a map of T-shaped intersection together with three cells used by the system shown in  FIG. 8 ; 
       FIGS. 10 and 11  illustrate a flowchart of operation executed by the system shown in  FIG. 8  to show a map in a portable terminal device; 
       FIG. 12  illustrates a block diagram of a portable terminal device used in a system for displaying a map according to yet another embodiment of the present invention; 
       FIG. 13  illustrates an appearance of the portable terminal device shown in  FIG. 12 ; 
       FIG. 14  illustrates a block diagram of operation executed by the map displaying system to display a map in the portable terminal device shown in  FIG. 12 ; and 
       FIG. 15  illustrates an appearance of a modified portable terminal device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described in reference to the accompanying drawings. 
   Referring to  FIG. 1 , illustrated is a system for displaying a map according to a first embodiment of the present invention. The map displaying system includes a host device  1  and a portable (mobile) terminal device  2 . The host device  1  may be located on the ground adjacent to an entrance/exit of a subway. The host device  1  provides wireless (radio) communication with the portable terminal device  2 . A technique in compliance with the Bluetooth standard is employed as the wireless (radio) communication technique. 
   As shown in  FIG. 1 , the host device  1  includes two Bluetooth transmission/reception units  11  and  12 , a control circuit  13  and a memory device  14 . Each of the Bluetooth transmission/reception units  11  and  12  is a unit for transmitting and receiving signals in compliance with the Bluetooth standard and has an antenna  11   a ,  12   a . The antennas  11   a  and  12   a  possess different directivities. An area (region) of signal transmission and reception by the antenna  11   a  is a semicircular, first cell, and an area of signal transmission and reception by the antenna  12   a  is a semicircular, second cell. The first and second cell are independent from each other. The memory device  14  stores map data in the form of image data. The map data includes two kinds of maps. One map is a ground map that shows a plat on the ground, with a direction towards a ground entrance/exit from a underground passage(way) of a subway system being at the top of the map. The other map is an underground map that shows a plat under the ground, with the direction towards the underground from the ground entrance/exit being at the top of the map. The maps indicate streets, banks, hotels, department stores, shops, and other conspicuous buildings with their names. The control circuit  13  reads the map data from the memory device  14  when the first Bluetooth transmission/reception device  11  receives a signal from a remote Bluetooth machine such as the portable terminal device  2 . The control circuit  13  then causes the first Bluetooth transmission/reception device  11  to transmit the map data to the Bluetooth machine. 
   The portable terminal device  2  is a mobile terminal machine that has a cellular phone function. As schematically illustrated in  FIG. 1 , the portable terminal device  2  includes a telephone signal transmission/reception part  31 , a Bluetooth transmission/reception part  32 , a display unit  33 , an operation unit  34 , a memory  35 , and a control circuit (CPU)  36 . The telephone transmission/reception unit  31  for wireless telephone communication has an antenna  31   a , a microphone  37  and a speaker  38 . The microphone  37  and speaker  38  are provided for telephone conversation. The Bluetooth transmission/reception device  32  is a signal transmission and reception unit that conforms to the Bluetooth standard. An antenna  32   a  extends from the Bluetooth transmission/reception device  32 . The control circuit  36  is connected to the telephone transmission/reception unit  31 , Bluetooth transmission/reception device  32 , display  33 , control panel  34  and memory  35 , and controls the overall operations of the portable terminal device  2 . 
   When a user of the portable terminal device  2  walks upstairs from an underground passage(way) of a subway and enters the area of the first cell as shown in  FIG. 2 , the portable terminal device  2  subscribes for a piconet as shown in  FIG. 3  (Step S 1 ). The host device  1  is a master and the portable terminal device  2  is a slave in the piconet. A subscription procedure for the piconet is defined in the Bluetooth standard so that the subscribing procedure will not be described here. The first Bluetooth transmission/reception device  11  in the host device  1  is activated to communicate with the Bluetooth transmission/reception device  32  in the portable terminal device  2  for the piconet subscription. 
   After the subscription procedure for the piconet is complete, the control circuit  13  of the host device  1  reads map data, which shows a ground map suited for the user present in the first cell, from the memory device  14  (Step S 2 ), and causes the Bluetooth transmission/reception device  11  to send the map data to the portable terminal device  2  (Step S 3 ). 
   Upon receiving the map data, the Bluetooth transmission/reception device  32  of the portable terminal device  2  transfers the map data to the control circuit  36 . The control circuit  36  transfers the map data to the display unit  33  and causes the display unit  33  to display the map such that the top of the map is shown at the top of the display unit  33  (Step S 4 ). The display  33  of the portable terminal device  2  shows the map as depicted in FIG.  4 . The top of the displayed map corresponds to the direction towards the ground exit from the underground facility. 
   It should be noted that the map displaying operation may not be done automatically, but by a certain operation made onto the control panel  34  by the user. 
   On the other hand, when the user of the portable terminal device  2  on the ground walks into the second cell area ( FIG. 2 ) in order to step down into the underground facility, the portable terminal device  2  subscribes for the piconet (Step S 1 ), as in the case of stepping up to the ground from the underground facility. The second Bluetooth transmission/reception device  12  of the host device  1  is then activated to communicate with the Bluetooth transmission/reception device  32  of the portable terminal device  2  for the piconet subscription. 
   After completing the subscribing procedure for the piconet, the control circuit  13  of the host device  1  reads map data, which shows an underground map suited for the user present in the second cell, from the memory device  14  (Step S 2 ). The control circuit  13  then causes the Bluetooth transmission/reception device  12  to send the map data to the portable terminal device  2  (Step S 3 ). 
   When the Bluetooth transmission/reception device  32  of the portable terminal device  2  receives the map data, the Bluetooth transmission/reception device  32  supplies the map data to the control circuit  36 . The control circuit  36  supplies the map data to the display unit  33  and causes the display unit  33  to show the subway facility map (underground map) such that the top of the map is shown at the top of the display screen (Step S 4 ). The top of the displayed map corresponds to the direction from the ground entrance to the underground facility. The top of the display screen  33  is generally directed in a direction in which the user of the portable terminal device  2  is walking (downward arrow in FIG.  2 ). The user is walking downstairs in this instance. 
   If the portable terminal device  2  immediately moves from the area of the first cell to the area of the second cell, the map data of ground map is transmitted to the portable terminal device  2  and subsequently a new piconet is established between the Bluetooth transmission/reception devices  12  and  32  (Step S 5 ) so that another map data of underground map is read and transmitted (Steps S 6  and S 7 ). The map data of underground map is, however, neglected by the portable terminal device  2  (Step S 8 ). Contrarily, when the portable terminal device  2  immediately moves into the area of the first cell from the area of the second cell, the map data of the underground map is transmitted to the portable terminal device  2  and subsequently a new piconet is established between the Bluetooth transmission/reception devices  11  and  32  so that the map data of ground map is also transmitted to the portable terminal device  2 . The map data of the ground map is, however, ignored by the portable terminal device  2 . The host device  1  handles both the first and second cells in the above described embodiment so that the host device  1  may be designed such that the host device  1  only sends the map data of the ground map when the host device  1  detects a fact that the portable terminal device  2  has moved to the second cell area from the first cell area within a predetermined period. Likewise, it is possible to design the host device  1  such that the host device  1  only sends the map data of underground map when the host device detects that the portable terminal device  2  has moved to the first cell area from the second cell area within a predetermined period. 
   Although the map data is only transmitted to the portable terminal device  2  in the above described embodiment, it is satisfactory to broadcast the same map data to other portable (mobile) terminal devices existing in the same cell as the portable terminal device  2 . 
   The above described system for displaying a map is applicable when the user enters or exits a department store. Referring to  FIG. 5 , the semicircular first cell outside the entrance/exit of the department store is used as the signal transmission/reception area of the antenna  11   a  and the opposite semicircular cell (second cell) inside the entrance/exit of the department store is used as the signal transmission/reception area of the antenna  12   a . The map data stored in the memory device  14  include a map of a first floor inside the department store and a map of streets outside the department store. The top of the map of the first floor is aligned with the perpendicular direction from the outside of the department store to the inside through the entrance/exit (direction in which the user of the portable terminal device  2  perpendicularly walks into the department store through the entrance/exit). The top of the map of the streets is aligned with the perpendicular direction from the inside of the department store to the outside. When the user of the portable terminal device  2  outside the department store walks towards the entrance/exit of the department store and steps in the first cell, the procedure shown in  FIG. 3  is carried out so that the map of the sales floor (first floor) inside the department store is shown in the display screen  33  of the portable terminal device  2 . The control circuit  36  causes the display to display the map such that the top of the map coincides with the top of the display screen. When the user of the portable terminal device  2  inside the department store walks towards the entrance/exit of the department store and steps in the second cell, on the other hand, the procedure shown in  FIG. 3  takes place so that the map of the streets outside the department store is shown in the display screen  33  of the portable terminal device  2 . The control circuit causes the display  33  to display the map such that the top of the map coincides with the top of the screen. 
   Referring to  FIG. 6 , illustrated is a system for displaying a map that is activated in accordance with different floors of the department store. In general, the department store has more than one floor and a customer goes to different floors by an elevator. The illustrated system can show maps of different floors, and includes a host device  41 , a portable terminal device  42  and a control circuit  43  of an elevator  44 . The elevator control circuit  43  causes the elevator  44  to move up and down in accordance with an operation made by a person in the elevator so as to stop the elevator  44  at a desired floor. 
   The host device  41  is similar to the host device  1  shown in  FIG. 1  except for having only one Bluetooth transmission/reception device. The host device  41  includes a Bluetooth transmission/reception device  51 , a control circuit  53  and a memory device  54 . An antenna  51   a  of the Bluetooth transmission/reception device  51  is provided in the elevator cage  44 , but other elements of the host device  41  may be provided either inside or outside the elevator cage  44 . The host device control circuit  53  is coupled with the elevator control circuit  43  via an interface (not shown). The elevator control circuit  43  supplies data of floor, on which the user of the portable terminal device  42  desires to get off, to the host device control circuit  53 . The memory device  54  stores map data of respective floors in the department store. The top of the each floor map is aligned with the perpendicular direction from the inside of the elevator to the floor. 
   The portable terminal device  42  has a structure similar to the portable terminal device  2  shown in FIG.  1 . Specifically, the portable terminal device  42  includes a telephone signal transmission/reception unit  61 , a Bluetooth transmission/reception unit  62 , a display unit  63 , an operation unit  64 , a memory  65 , a control circuit  66 , a telephone microphone  67  and a telephone speaker  68 . Like the system shown in  FIG. 1 , wireless communication takes place between the host device  41  and portable terminal device  42  using the Bluetooth technique. The interior of the elevator cage  44  is an area of signal transmission and reception (i.e., cell) covered by the antenna  51   a.    
   Referring to  FIG. 7 , a subscribing operation of the portable terminal device  42  for the piconet is executed when the user of the portable terminal device  42  steps into the elevator cage  44  (Step S 11 ). In the piconet, the host device  41  is a master and the portable terminal device  42  is a slave. The Bluetooth transmission/reception device  51  of the host device  41  is activated to communicate with the Bluetooth transmission/reception device  62  of the portable terminal device  42  for the piconet subscription. 
   When a door of the elevator closes (Step S 12 ), the control circuit  43  supplies data of desired floor to the control circuit  53  of the host device  41  (Step S 13 ). Upon receiving the data of desired floor, the control circuit  53  retrieves map data of the desired floor from the memory device  54  (Step S 14 ). The control circuit  53  then causes the Bluetooth transmission/reception device  51  to transmit the map data to the portable terminal device  42  (Step S 15 ). 
   Upon receiving the map data, the Bluetooth transmission/reception device  62  of the portable terminal device  42  supplies the map data to the control circuit  66 . Subsequently the control circuit  66  feeds the map data to the display unit  63  and causes the display unit  63  to display a map of the floor at which the elevator will stop (Step S 16 ). The control circuit  66  causes the display unit  63  to display the map such that the top of the map coincides with the direction penetrating the elevator cage door at right angle from the inside of the elevator cage  44  towards the floor. 
   Eventually the elevator  44  arrives at the desired floor and stops (Step S 17 ). After the door opens (Step S 18 ), the program returns to Step S 12  because the door closes. The procedure from Steps S 13  to S 16  is then repeated to cause the display unit  63  to display a map of a next desired floor. 
   Referring to  FIG. 8 , illustrated is a system for displaying a map when a user of the portable terminal device  2  walks in a T-shaped intersection under the ground of a subway facility. A path P 1  meets another path P 2  perpendicularly thereby forming the T-shaped intersection. A host device  71  of the map displaying system includes three Bluetooth transmission/reception devices  81  to  83 , a control circuit  84  and a memory device  85 . The first Bluetooth transmission/reception device  81  can communicate with a portable terminal device in the first cell (FIG.  9 ), i.e., a circular area of signal transmission and reception covered by an antenna  81   a  provided on the path P 1 . The second Bluetooth transmission/reception device  82  can communicate with a portable terminal device in the second cell, i.e., a circular area of signal transmission and reception covered by an antenna  82   a  provided on the path P 2 . The third Bluetooth transmission/reception device  83  can communicate with a portable terminal device in the third cell, i.e., a circular area of signal transmission and reception covered by an antenna  83   a  provided on the path P 2  opposite the second cell relative to the path P 1 . The first to third cells are established in the vicinity of the intersection of the paths P 1  and P 2 . When viewed from the path P 1 , the second cell is present on the left side of the intersection and the third cell is present on the right side. 
   The memory device  85  stores three map data in the form of image data. The first map data shows an underground map such that the top of the map coincides with the direction from the first cell to the intersection, the second map data shows an underground map such that the top of the map coincides with the direction from the second cell to the intersection, and the third map data shows an underground map such that the top of the map coincides with the direction from the third cell to the intersection. 
   The portable terminal device  2  shown in  FIG. 1  is used in the system shown in FIG.  8 . 
   Operation of the portable terminal device  2  for displaying a map when the user of the portable terminal device  2  walks in the intersection along the path P 1  or P 2  will be described. 
   Referring to  FIG. 10 , the control circuit  36  of the portable terminal device  2  determines whether the portable terminal device  2  exists in the first cell (Step S 31 ). If the portable terminal device  2  exists in the first cell, the control circuit  36  can obtain information of existence of the portable terminal device  2  in the first cell from the host device  71  because the portable terminal device  2  performs the subscribing operation for the piconet. Likewise, if the portable terminal device  2  exists in the second (or third) cell, the control circuit  36  can obtain information of existence of the portable terminal device  2  in the second (or third) cell from the host device  71 . 
   When the portable terminal device  2  is present in the first cell, the portable terminal device  2  receives first map data from the host device  71  (Step S 32 ). The first map data is map data suited for the user in the first cell. An underground map derived from the first map data is then displayed in the display screen  33  of the portable terminal device  2  (Step S 33 ). The control circuit  36  causes the display to show the map such that the top of the map coincides with the top of the display screen. The top of the map is aligned with the direction from the first cell to the intersection. 
   After Step S 33 , the control circuit  36  determines whether the portable terminal device  2  is present in the second cell (Step S 34 ). In other words, Step S 34  determines whether the user of the portable terminal device  2  who has stepped out the first cell now walks into the second cell by making the left turn at the intersection. If the portable terminal device  2  (or the user) exists in the second cell, the first map data received at Step S 32  is converted to map data suited for the user in the second cell (Step S 35 ). Specifically, the first map data is converted such that the map in the screen  33  of the portable terminal device  2  is turned 90 degrees to the right. The map prepared from the converted map data is then displayed in the screen  33  (Step S 36 ). The top of the map in the screen  33  coincides with the direction from the intersection to the second cell because the control circuit  36  causes the display to show the 90-degree turned map such that the new top of the map is aligned with the top of the display screen. 
   When the control circuit  36  determines at Step S 34  that the portable terminal device  2  does not exist in the second cell, the control circuit  36  then determines whether the portable terminal device  2  exists in the third cell (Step S 37 ). In other words, it is determined whether the user of the portable terminal device  2  walks from the first cell to the third cell by making the right turn at the intersection. If the portable terminal device  2  is present in the third cell, the first map data received at Step S 32  is converted (Step S 38 ). Specifically, the map data is converted such that the map is turned 90 degrees to the left in the screen  33  of the portable terminal device  2 . The map prepared from the converted map data is then displayed in the screen  33  (Step S 39 ). The top of the map coincides with the direction from the intersection to the third cell. 
   If the control circuit  36  determines at Step S 37  that no portable terminal device  2  exists in the third cell, the program returns to Step S 34  to determine whether the portable terminal device  2  exists in the second cell. 
   When it is determined at Step S 31  that the portable terminal device  2  does not exist in the first cell, the control circuit  36  determines whether the portable terminal device  2  exists in the second cell (Step S 40 , FIG.  11 ). If the portable terminal device  2  is present in the second cell, the portable terminal device  2  receives second map data from the host device  71  (Step S 41 ). The second map data is map data suited for the user of the portable terminal device in the second cell. A map prepared from the second map data is then displayed in the screen  33  of the portable terminal device  2  (Step S 42 ). The top of the displayed map is aligned with the direction from the second cell to the intersection. 
   After Step S 42 , the control circuit  36  determines whether the portable terminal device  2  exists in the first cell (Step S 43 ). In other words, it is determined whether the user of the portable terminal device  2  walks in the first cell from the second cell by making the right turn at the intersection. If the portable terminal device (or the user) exists in the first cell, the second map data received at Step S 41  is converted (Step S 44 ). Specifically, the second map data is converted such that the map in the screen  33  of the portable terminal device  2  is turned 90 degrees. The map prepared from the converted second map data is then displayed in the screen  33  (Step S 45 ). The top of the map coincides with the direction from the intersection to the first cell (or the path P 1 ). 
   If the control circuit  36  determines at Step S 43  that the portable terminal device  2  does not exist in the first cell, the control circuit determines whether the portable terminal device  2  exists in the third cell (Step S 46 ). In other words, it is determined whether the user of the portable terminal device  2  walks straight into the third cell from the second cell. When the portable terminal device  2  is present in the third cell, the direction (posture) of the currently displayed map is maintained. 
   When the control circuit  36  determines at Step S 46  that the portable terminal device  2  does not exist in the third cell, the program returns to Step S 43  to determine again whether the portable terminal device  2  exists in the first cell. 
   When the control circuit  36  determines at Step S 40  that the portable terminal device  2  does not exist in the second cell, the control circuit determines whether the portable terminal device  2  exists in the third cell (Step S 47 ). If the portable terminal device  2  exists in the third cell, the portable terminal device  2  receives third map data from the host device  71  (Step S 48 ). The third map data is map data suited for the user in the third cell. A map prepared from the third map data is then shown in the display  33  of the portable terminal device  2  (Step S 49 ). The top of the map coincides with the direction from the third cell to the intersection. 
   After Step S 49 , the control circuit  36  determines whether the portable terminal device  2  exists in the first cell (Step S 50 ). In other words, it is determined whether the user of the portable terminal device  2  walks in the first cell from the third cell by making the left turn at the intersection. If the portable terminal device (or the user) is in the first cell, the control circuit converts the third map data received at Step S 48  (Step S 51 ). Specifically, the third map data is converted such that the map is turned 90 degrees to the right. A map prepared from the converted third map data is then displayed in the screen  33  of the portable terminal device  2  (Step S 52 ). The top of the map coincides with the direction from the intersection to the first cell (or the path P 1 ). 
   If the control circuit  36  determines at Step S 50  that the portable terminal device  2  does not exist in the first cell, the control circuit determines whether the portable terminal device  2  exists in the second cell (Step S 53 ). In other words, it is determined whether the user of the portable terminal device  2  walks straight into the second cell from the third cell. When the portable terminal device  2  is present in the second cell, the direction (posture) of the currently displayed map is maintained. 
   If the control circuit  36  determines at Step S 53  that the portable terminal device  2  does not exist in the second cell, the program returns to Step S 50  and the control circuit  36  determines whether the portable terminal device  2  exists in the first cell. 
   Therefore, when the user of the portable terminal device  2  moves from a certain location to another location through the intersection, the portable terminal device  2  can show a map in the screen  33  such that the top of the displayed map always corresponds to the moving direction of the user. 
   Although the above described embodiment deals with the case where the user of the portable terminal device  2  passes through a T intersection, the present invention is also applicable to a case where the user passes through an L-shaped or X-shaped intersection. If the host device can inform the portable terminal device of a turning angle at the intersection (how much the path bends), the map may be turned by a degree corresponding to the informed turning angle. It is not always necessary to turn the map 90 degrees. 
   Referring to  FIG. 12 , illustrated is a portable terminal device  40  having a geomagnetic sensor  39 . The portable terminal device  40  is similar to the portable terminal device  2  shown in  FIG. 1  except for having the geomagnetic sensor  39 . The portable terminal device  40  includes a telephone signal transmission/reception unit  31 , a Bluetooth transmission/reception device  32 , a display unit  33 , an operation unit  34 , a memory  35 , a control circuit (CPU)  36 , a microphone  37 , a speaker  38  and the geomagnetic sensor  39 . As illustrated in  FIG. 13 , the geomagnetic sensor  39  is located below the display  33  on the front face of the portable terminal device  40 . A reference direction of the geomagnetic sensor  39  is the north, and the geomagnetic sensor  39  detects the direction of the portable terminal device  40 , i.e., in which direction the head of the portable terminal device  40  is pointing. 
   When the user of the portable terminal device  40  walks upstairs from the underground (subway walkway) towards the ground and enters the first cell (FIG.  2 ), the portable terminal device performs the subscribing operation for the piconet (Step S 1 ) as shown in FIG.  3 . The Bluetooth transmission/reception device  11  of the host  1  is then activated to communicate with the Bluetooth transmission/reception device  32  of the portable terminal device  40  for the piconet subscription. Upon completing the piconet subscribing operation, the control circuit  13  of the host device  1  reads map data suitable for the user in the first cell from the memory device  14  (Step S 2 ) and causes the Bluetooth transmission/reception device  11  to transmit the map data to the portable terminal device  40  (Step S 3 ). 
   Upon receiving the map data (Step S 61  in FIG.  14 ), the Bluetooth transmission/reception device  32  of the portable terminal device  40  supplies the map data to the control circuit  36 . The control circuit  36  supplies the map data to the display unit  33  and causes the display unit to show a map in the display screen such that the top of the map is aligned with the top of the display screen as shown in  FIG. 13  (Step S 62 ). The top of the map displayed in the portable terminal device  40  therefore corresponds the direction from the underground walkway to the entrance/exit of the walkway on the ground. 
   The control circuit  36  then obtains direction data of the portable terminal device  40  (in which direction the portable terminal device  40  is directed, or how much the direction of the portable terminal device  40  is deviated from the reference direction, i.e., the north) from the geomagnetic sensor  39  (Step S 63 ) and converts (rotates) the map data in accordance with the obtained direction data (Step S 64 ). The control circuit  36  feeds the converted map data to the display unit  33  and causes the display unit  33  to display the map on the basis of the converted map data (Step S 65 ). Therefore, the direction of the map top in the display screen  33  is adjusted to always align with the direction from the underground walkway to the ground entrance/exit of the walkway, even if the longitudinal direction of the portable terminal device  40  is deviated from the direction from the underground walkway to the ground entrance/exit of the walkway. The deviation from the portable terminal device  40  from the north is adjusted (counterbalanced) by the geographic sensor  39  and control circuit  36 . 
   Steps S 63  to S 65  are repeated after Step S 65 . Thus, the direction of the displayed map is continuously adjusted such that the direction from the underground walkway to the ground entrance/exit always is aligned with (matches) the direction of the map displayed in the screen  33  regardless of the direction of the portable terminal device  40 . 
   When the user of the portable terminal device  40  enters the second cell ( FIG. 2 ) to step downstairs to the underground, a map of the underground is displayed in the screen  33 . The top of the map always is aligned with the direction from the ground entrance/exit of the underground walkway to the underground regardless of the direction of the portable terminal device  40 . 
   Although the geomagnetic sensor  39  is provided as the direction detection means for the portable terminal device  40  in the above described embodiment, other types of direction detection means may be employed. For instance, a CCD camera  91  and four rods  92   a  to  92   d  may be provided in or on the portable terminal device  40  as illustrated in FIG.  15 . The four rods  92   a  to  92   d  are located around a lens of the CCD camera  91  at equal intervals. Shadows of the rods  92   a  to  92   d  made on the portable terminal device  40  by the sunlight, moonlight or particular starlight (e.g., light from the North Star) are detected by the CCD camera  91  when the portable terminal device  40  is held horizontally. The direction of the portable terminal device  40  is then calculated on the basis of relationship between the shadows of the sunlight (or moonlight or particular starlight) and day-and-time. The relationship between the shadows of the sunlight (or moonlight or particular starlight) and day-and-time is stored in the portable terminal device beforehand. 
   It should be noted that although the wireless communication technique in compliance with the Bluetooth standard is utilized for the communication between the host device and portable terminal device in the above described embodiments, other wireless communication technique such as IrDA (Infrared Data Association), HomeRF (Home Radio Frequency) and IEEE 802.11 may be utilized. The rods  92   a  to  92   d  may be replaced with any projections as long as the projections can make shadows. 
   As described above, the system of the present invention displays a map such that the moving direction of the portable terminal device is aligned with the top of the displayed map. Therefore, a user of the portable terminal device can easily understand relationship between a moving direction of the user and the top of the map (direction of the map) in the display. 
   This application is based on Japanese Patent Application No. 2000-352508, and the entire disclosure thereof is incorporated herein by reference.