FGDC-STD-014.7-2008

Geographic Information Framework Data Content 

Standard 

Part 7: Transportation Base 

May 2008 
ii

Federal Geographic Data Committee 

Established by Office of Management and Budget Circular A-16, the Federal Geographic Data 

Committee (FGDC) promotes the coordinated development, use, sharing, and dissemination of 

geographic data. 

The FGDC is composed of representatives from the Departments of Agriculture, Commerce, 

Defense, Education, Energy, Health and Human Services, Homeland Security, Housing and 

Urban Development, the Interior, Justice, Labor, State, and Transportation, the Treasury, and 

Veteran Affairs; the Environmental Protection Agency; the Federal Communications Commission; 

the General Services Administration; the Library of Congress; the National Aeronautics and 

Space Administration; the National Archives and Records Administration; the National Science 

Foundation; the Nuclear Regulatory Commission; the Office of Personnel Management; the Small 

Business Administration; the Smithsonian Institution; the Social Security Administration; the 

Tennessee Valley Authority; and the U.S. Agency for International Development. Additional 

Federal agencies participate on FGDC subcommittees and working groups. The Department of 

the Interior chairs the committee. 

FGDC subcommittees work on issues related to data categories coordinated under the circular. 

Subcommittees establish and implement standards for data content, quality, and transfer; 

encourage the exchange of information and the transfer of data; and organize the collection of 

geographic data to reduce duplication of effort. Working groups are established for issues that 

transcend data categories. 

For more information about the committee, or to be added to the committee's newsletter mailing 

list, please contact: 

Federal Geographic Data Committee Secretariat 

c/o U.S. Geological Survey 

590 National Center 

Reston, Virginia 22092 

Facsimile: (703) 648-5755 

Internet (electronic mail): fgdc@usgs.gov 

 World Wide Web: http://www.fgdc.gov
Federal Geographic Data Committee FGDC-STD-014.7-2008 

Geographic Information Framework Data Content Standard 

Part 7: Transportation Base

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Contents 

Introduction................................................................................................................................... iv

1 Scope........................................................................................................................................... 1

2 Conformance............................................................................................................................... 1

3 Normative references................................................................................................................. 2

4 Maintenance authority ............................................................................................................... 2

4.1 Level of responsibility...................................................................................................... 2

4.2 Contact information ......................................................................................................... 2

5 Terms and definitions ................................................................................................................ 2

6 Symbols, abbreviated terms, and notations............................................................................ 5

7 Requirements.............................................................................................................................. 5

7.1 Transportation base model ............................................................................................. 5

7.2 Transportation feature model.......................................................................................... 6

7.3 Transportation segmentation model .............................................................................. 7

7.3.1 Introduction....................................................................................................................... 7

7.3.2 TranSeg ............................................................................................................................. 7

7.3.3 TranPoint........................................................................................................................... 8

7.3.4 TranPath ............................................................................................................................ 9

7.3.5 Transportation system................................................................................................... 11

7.4 Transportation event model .......................................................................................... 14

7.4.1 LinearAttributeEvent ...................................................................................................... 16

7.4.2 PointAttributeEvent........................................................................................................ 16

7.4.3 LinearFeatureEvent........................................................................................................ 16

7.4.4 PointFeatureEvent.......................................................................................................... 16

7.4.5 Attributes for events ...................................................................................................... 18

Annex A (informative) Equivalencies ........................................................................................ 20

Annex B (normative) Package: Linear reference systems...................................................... 22

B.1 Semantics........................................................................................................................ 22

B.2 LR_PositionExpression ................................................................................................. 22

B.2.1 Semantics........................................................................................................................ 22

B.2.2 Attribute: measure : Measure........................................................................................ 22

B.2.3 Role: LRM : LR_LinearReferenceMethod..................................................................... 22

B.2.4 Role: referent [0..1] : LR_ReferenceMarker ................................................................. 23

B.2.5 Role: referenceDomain : LR_Element .......................................................................... 23

B.2.6 Role: offset[0..1] : LR_OffsetExpression ..................................................................... 23

B.3 LR_LinearReferenceMethod.......................................................................................... 24

B.3.1 Semantics........................................................................................................................ 24

B.3.2 Attribute: name : CharacterString ................................................................................ 24

B.3.3 Attribute: type : CharacterString................................................................................... 24

B.3.4 Attribute: units : UnitOfMeasure................................................................................... 24

B.3.5 Attribute: offsetUnits : UnitOfMeasure......................................................................... 24

B.3.6 Attribute: positiveOffsetDirection : LR_OffsetDirection = "right"............................. 24

B.3.7 Role: marker[1..*] : LR_ReferenceMarker .................................................................... 25

B.3.8 Role: referenceElement[1..*] : LR_Element ................................................................. 25

B.3.9 Operation: project .......................................................................................................... 25
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B.4 LR_OffsetDirection......................................................................................................... 25

B.5 LR_ReferenceMarker...................................................................................................... 26

B.5.1 Semantics........................................................................................................................ 26

B.5.2 Attribute: name : CharacterString ................................................................................ 26

B.5.3 Attribute: type : CharacterString................................................................................... 26

B.5.4 Attribute: position[0..1] : GM_Point.............................................................................. 26

B.5.5 Attribute: location[0..1] : LR_PositionExpression ...................................................... 26

B.6 LR_Feature...................................................................................................................... 27

B.7 LR_Element..................................................................................................................... 27

B.7.1 Semantics........................................................................................................................ 27

B.7.2 Role: datumMarkers[1..*] : LR_ReferenceMarker........................................................ 27

B.8 LR_OffsetReference....................................................................................................... 28

B.9 LR_OffsetExpression..................................................................................................... 28

B.9.1 Semantics........................................................................................................................ 28

B.9.2 Attribute: offsetReference : LR_OffsetReference ....................................................... 28

B.9.3 Attribute: offset[0..1] : Number ..................................................................................... 28

Annex C (informative) Bibliography .......................................................................................... 29

Figures 

Figure 1 – Transportation base model ........................................................................................ 6

Figure 2 – Transportation feature type hierarchy ...................................................................... 7

Figure 3 – Relationships among TranSeg, TranPoint, and TranPath....................................... 8

Figure 4 – Proper use of TranPoint class ................................................................................... 9

Figure 5 – TranPath model ......................................................................................................... 10

Figure 6 – Transportation event model (1)................................................................................ 14

Figure 7 – Transportation event model (2)................................................................................ 15 

Figure A.1 – Sample datasets representing the same segment of road................................ 20 

Figure B.1 – LRS classes............................................................................................................ 23

Figure B.2 – LR_PositionExpression......................................................................................... 24

Figure B.3 – LR_LinearReferenceMethod ................................................................................. 25

Figure B.4 – LR_OffsetDirection ................................................................................................ 26

Figure B.5 – LR_ReferenceMarker............................................................................................. 26

Figure B.6 – LR_Feature ............................................................................................................. 27

Figure B.7 – LR_Element ............................................................................................................ 27

Figure B.8 – LR_OffsetExpression ............................................................................................ 28

Tables 

Table 1 – Data dictionary for transportation system objects.................................................. 11

Table 2 – Data dictionary for transportation event objects..................................................... 18
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Foreword 

Geographic information, also known as geospatial information, both underlies and is the subject 

of much of the political, economic, environmental, and security activities of the United States. In 

recognition of this, the United States Office of Management and Budget issued Circular A-16 

(revised 2002), which established the Federal Geographic Data Committee (FGDC) as a 

coordinating organization. 

Work on this standard started under the Geospatial One-Stop e-Government initiative. The 

standard was developed with the support of the member agencies and organizations of the 

FGDC and aids in fulfilling a primary objective of the National Spatial Data Infrastructure (NSDI), 

that is, creation of common geographic base data for seven critical data themes. The seven core 

data themes are considered framework data of critical importance to the spatial data 

infrastructure. 

As the Geographic Information Framework Data Content Standard was developed using public 

funds, the U.S. Government will be free to publish and distribute its contents to the public, as 

provided through the Freedom of Information Act (FOIA), Part 5 United States Code, Section 552, 

as amended by Public Law No. 104-231, “Electronic Freedom of Information Act Amendments of 

1996”. 
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Introduction 

The primary purpose of this part of the Geographic Information Framework Data Content 

Standard is to support the exchange of transportation data. This part seeks to establish a 

common baseline for the semantic content of transportation databases for public agencies and 

private enterprises. It also seeks to decrease the costs and simplify the exchange of 

transportation data among local, Tribal, State, and Federal users and producers. That, in turn, 

discourages duplicative data collection. Benefits of adopting this part of the standard also include 

the long-term improvement of the geospatial transportation data within the community, improved 

integration of safety, emergency response, and enforcement data, and streamlines maintenance 

procedures. 
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Geographic Information Framework Data Content Standard 

Part 7: Transportation Base

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1 Scope 

The Geographic Information Framework Data Content Standard, Part 7: Transportation Base 

defines the data model for describing transportation systems components of transportation 

systems for five modes that compose the Transportation theme of the NSDI. The primary 

purpose of this part of the standard is to support the exchange of transportation data related to 

transportation systems. It is the intent of the Transportation Base part to set a common baseline 

that will ensure the widest utility of transportation data for the user and producer communities 

through enhanced data sharing and the reduction of redundant data production. 

At a high level, the transportation system described in this part of the Framework Data Content 

Standard is made up of transportation features, which can have geographic locations and 

characteristics. These transportation features can be interconnected in various ways and across 

several modes to represent transportation networks for path finding/routing applications. While 

the design team has considered the need for path finding applications, the level of data required 

by such applications is beyond the scope of many organizations. Specifically, many State and 

local government agencies do not have adequate data for routing purposes, and they do not have 

the budget to create and maintain this data. It is expected that the content in the part will support 

the development of specialized networks for routing applications, but this level of information is 

not a requirement of the data standard. 

This part of the standard can be implemented using a variety of software packages and is 

designed to accommodate data encoded without geometry as well as to support the exchange of 

data encoded in a variety of geographic information systems. The part accommodates assets 

associated with the transportation system that are typically used for navigation, safety, and 

measurement. 

The part applies to NSDI framework transportation data produced or disseminated by or for the 

Federal Government. According to Executive Order 12906, Coordinating Geographic Data 

Acquisition and Access: The National Spatial Data Infrastructure, Federal agencies collecting or 

producing geospatial data, either directly or indirectly (for example, through grants, partnerships, 

or contracts with other entities), shall ensure, prior to obligating funds for such activities, that data 

will be shared in a manner that meets all relevant standards adopted through the Federal 

Geographic Data Committee (FGDC) process. 

The Geographic Information Framework Data Content Standard for the Transportation theme is 

comprised of six parts: Base, Air, Rail, Road, Transit, and Inland Waterways. While there are 

enough differences in the transportation modes to warrant separate parts, the reader should be 

aware that there are many similarities. The six parts are meant to complement each other and to 

represent a complete, if somewhat basic model of a whole transportation system. 

The Transportation Base part integrates the five modes of transportation systems: air, rail, road, 

transit, and water. To accommodate multi-modal transportation systems, transportation points 

and transportation paths are instantiable, whereas transportation segments are not. This allows 

the linear segments of each mode to be mode-specific (for example, roadway segments) but 

allows them to be connected to segments from other modes. A multi-modal node such as a 

passenger rail station could be used to connect roadway segments and rail segments. In this 

case, it would be represented as a transportation point instead of a roadway point or rail point. 

Alternatively, it could be modeled as both a roadway point and a rail point, with the two being 

equivalenced. A transportation path instance would be able to use roadway segments and rail 

segments to define a multi-modal route. 

2 Conformance 

This thematic part includes a data dictionary/model based on the conceptual schema presented 

below. To conform to this part, the user shall satisfy the requirements of the data 

dictionary/model. The user's conforming dataset shall include a value for each mandatory 
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element, and a value for each conditional element for which the condition is true. It may contain 

values for any optional element. The data type of each value shall be that specified for the 

element in the data dictionary/model and the value shall lie within the specified domain. This part 

only specifies the special requirements of conformance for a dataset containing transportation 

information. Conformance to the standard requires additional actions specified in the Base 

Document (Part 0) and the appropriate modal parts for Air (Part 7a), Rail (Part 7b), Roads (Part 

7c), Transit (Part 7d), and Inland Waterways (Part 7e). 

3 Normative references 

Annex A of the Base Document (Part 0) lists normative references applicable to two or more parts 

of the standard, including those other than the transportation parts. No additional normative 

references are specified for the Transportation Base (Part 7). Informative references applicable to 

two or more transportation parts only are listed in Annex C of the Transportation Base part. 

Annex D of the Base Document lists informative references applicable to two or more of the parts, 

including those other than the transportation parts. 

4 Maintenance authority 

4.1 Level of responsibility 

The FGDC is the responsible organization for coordinating work on all parts of the Geographic 

Information Framework Data Content Standard. The United States Department of Transportation 

(USDOT), working with the FGDC, is the responsible organization for coordinating work on the 

Geographic Information Framework Data Content Standard, Part 7: Transportation Base and 

subparts (Parts 7a, 7b, 7c, and 7d, excluding 7e) and is directly responsible for development and 

maintenance of the transportation parts (excluding 7e) of the Framework Data Content Standard. 

4.2 Contact information 

Address questions concerning this part of the standard to: 

Federal Geographic Data Committee Secretariat 

c/o U.S. Geological Survey 

590 National Center 

Reston, Virginia 20192 USA 

Telephone: (703) 648-5514 

Facsimile: (703) 648-5755 

Internet (electronic mail): gdc@fgdc.gov

WWW Home Page: http://fgdc.gov

5 Terms and definitions 

Definitions applicable to this part or multiple transportation parts of the standard are listed here. 

More general terms and definitions can be found in the Base Document (Part 0) of the standard. 

Other terms and definitions specific to a particular transportation mode are listed within the modal 

part of the standard. Users are advised to consult these documents for a complete set of 

definitions. 

5.1 

anchor point 

physical location in the field that can be unambiguously described so that it can be clearly located 

in the real world using its description [NCHRP 20-27(2)] 

NOTE An anchor point is a link between the computer representation of the road system and the real 

world. 
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5.2 

distance expression 

linear distance measured along a linear element

NOTE Distance expression is used as a component of a position expression. 

5.3 

entity 

feature that has separate and distinct existence and objective or conceptual reality 

5.4 

event 

mechanism for locating an attribute value or feature along a transportation feature

5.5 

event model 

part of the transportation model that defines a manner in which to model attributes that may have 

values that change along the length of a segment or path 

5.6 

feature event 

way of specifying the linear location of a feature along a transportation segment or 

transportation path

NOTE The located feature can have its own attributes, including its own (optional) geometry, 

independent of the geometry of any transportation segment or transportation path along which it is linearly 

referenced, for example, a bridge might be located with a feature event so that it can have attributes such as 

type, length, and year of construction and its own spatial representation, either as a point, line, or polygon (it 

may have all three) as well as being linearly referenced along a transportation segment or transportation 

path. 

5.7 

linear element 

underlying curvilinear element along which a linearly referenced measure is taken 

NOTE This is consistent with ISO 19133. 

5.8 

linear event 

event that occurs for an interval along the length of a linear feature 

NOTE The location of a linear event is specified by a start and end position expression. 

5.9 

linear location 

location that is specified as a distance along a one-dimensional linear element, such as a 

roadway, specified with a single coordinate, whose coordinate axis is the linear element itself 

5.10 

linear reference 

description of a location using a one-dimensional measurement along a linear element based 

upon the rules and units of some linear reference method 
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5.11 

offset 

optional part of a linearly referenced position expression which specifies the lateral distance left 

or right of the linear element being measured [ISO 19133] 

5.12 

point event 

event that occurs at a single position along a linear feature 

NOTE The location of a point event is specified by a single position expression. 

5.13 

position expression 

expression used to describe a position using linear referencing and comprised of a measured 

value (distance expression), the curvilinear element being measured (linear element), the 

method of measurement (LRM), and an optional lateral offset (offset expression) 

5.14 

referent 

known location from which a relative measurement can be made 

NOTE Referents are used in the distance expression of a position expression, for example, a milepost 

or reference post along a highway. 

5.15 

road point 

road segment terminus in the road segmentation model 

5.16 

road segment 

continuous nonbranching linear section of a road 

5.17 

road system 

part of the transportation system that relates to roads or their appurtenances such as road 

signs or signals 

5.18 

route 

ordered list of transportation segments 

5.19 

route 

‹transit› collection of patterns in revenue service and with a common identifier 

5.20 

transportation feature 

TranFeature 

representation of transportation entities that include transportation segmentation model

features, as well as other features relevant to transportation 
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5.21 

transportation path 

TranPath 

ordered list of whole or partial sections of the physical transportation system (that is to say, 

transportation segments) 

5.22 

transportation point 

TranPoint 

topological connection between transportation segments

5.23 

transportation segment 

TranSeg 

linear section of the physical transportation network 

NOTE A transportation segment shall be continuous (no gaps) and cannot branch; no mandates are 

provided on how to segment the transportation network except that a data provider adopt a consistent 

method. 

5.24 

transportation segmentation model 

set of transportation features (TranPath, TranPoint, and TranSeg) and their topological 

relationships which together define all possible movements through the transportation system

5.25 

transportation system 

set of components that allow the movement of goods and people between locations 

6 Symbols, abbreviated terms, and notations 

The following symbols, abbreviations, and notations are common to two or more transportation 

parts of the Framework Data Content Standard. More symbols, abbreviations, and notations 

applicable to multiple parts, including the transportation parts, are listed in the Base Document 

(Part 0). Those specific to a particular transportation mode are listed in that respective part. 

DOT – Department of Transportation 

GDF – Geographic Data Files 

7 Requirements 

7.1 Transportation base model 

Transportation entities are represented as TranFeatures. The transportation network is 

represented by TranSegs, TranPoints, and TranPaths. TranFeatures can have attributes. For 

linear TranSegs and TranPaths, if the values for these attributes can change along the length of 

the feature, the attributes are represented by AttributeEvents. FeatureEvents allow Features to 

be linearly located along TranSegs and/or TranPaths. See Figure 1. 
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Figure 1 – Transportation base model 

7.2 Transportation feature model 

Many transportation features have certain characteristics in common, such as linear geometries, 

a connective nature, and a system for indexing these real world features. In this part of the 

standard, rail, road, and transit modes share a common model for representation shown in Figure 

2. TranFeature is simply an extension of Feature that includes any and all transportation 

features. TranFeature has three explicit feature subclasses: TranPath, TranSeg, and TranPoint 

to represent the Transportation Segmentation Model. These three feature subclasses have 

analogues in the rail, road, transit, and waterway modes of transportation. All other transportation 

related real world entities are represented as instances of TranFeature or user-defined 

TranFeature subtypes. 
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Figure 2 – Transportation feature type hierarchy 

7.3 Transportation segmentation model 

7.3.1 Introduction 

The transportation segmentation model is the set of transportation features and their topological 

relationships which together define all possible movements through the transportation system. It 

can be broken up into segments called TranSegs. TranSegs represent individual pieces of the 

physical network, such as that part of Main Street which exists between First and Second 

Avenue. It is highly recommended that TranSegs be topologically connected by TranPoints. 

TranPoints merely serve to connect two TranSegs. TranPaths prescribe a usage of part of the 

transportation network. They represent a path through a set of whole or partial TranSegs, such 

as Route 66 or Bus Route 101. 

7.3.2 TranSeg 

TranSeg represents a linear section of the physical transportation network designed for, or the 

result of, human or vehicular movement. As shown in Figure 3, TranSeg extends TranFeature. 

Within this part of the standard, TranSeg may be defined in a variety of ways depending on mode 

and business application. It is left to the data creator to decide how to segment their 

transportation system in a manner that supports their organizational functions. A single TranSeg 
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can represent an entire segment between two points, or, a separate TranSeg can be defined for 

each direction of travel. Defining how and where segments are defined is dictated by the need of 

the application and the dataset being exchanged. 

TranSeg can have geometry of type GM_Curve as defined in ISO 19107. According to ISO 

19107, GM_Curve extends GM_OrientabletableCurve and therefore, has direction. The direction 

of a TranSeg is determined by its “from” and “to” TranPoints. TranSeg can also have a topology 

of type TP_DirectedEdge as defined in ISO 19107. TP_DirectedEdge has been introduced to 

facilitate the representation of feature topology through its combinatorial structures independent 

of its geometry. This has practical application within the Rail, Roads, and Transit parts as 

providers of those data may choose to represent only topology, without geometry, for rapid 

network tracing. Users are recommended to consult each modal part of the standard for more 

specific information. 

The relationships between TranSeg and TranPoint in Figure 3 show that each TranSeg is 

recommended to have a startPoint and endPoint. 

7.3.3 TranPoint 

The sole purpose of TranPoints is to provide the topological connection between TranSegs. It is 

highly recommended that each TranSeg have exactly one start TranPoint and one end TranPoint. 

This will help insure that the resultant set of TranSegs forms a complete coverage of the 

transportation system without gaps or overlaps. For exchanging datasets without such explicit 

connectivity, TranPoints can be considered to be optional. If a roadway transportation network is 

segmented at all roadway intersections, each TranSeg represents the physical roadway between 

two intersections and the TranPoints correspond to intersection locations. If instead, the 

transportation network is segmented into exactly five-mile long TranSegs, there may not be a 

physical entity where the resultant TranPoints occur. An intersection shall be represented as a 

Transportation Feature rather than a TranPoint. This allows flexibility in defining the intersection 

geometry as being a point, an area, or both. 

Figure 3 – Relationships among TranSeg, TranPoint, and TranPath 

Figure 4 illustrates a TranSeg bounded by two TranPoints, A and B. Point C represents the 

location of some real world entity such as an intersection or a bridge somewhere along the 

TranSeg. Point D represents the location of another entity along the TranSeg, but offset a lateral 

distance to one side. Because C and D do not terminate or represent the topological connection 

between TranSegs, they shall not be represented as TranPoints. Instead, if they represent real 
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world entities (with attributes), they shall be represented as Transportation Features. 

FeatureEvents can be used to define their location along and optionally offset from a TranSeg. 

Alternatively, Points C and D can be represented as AttributeEvents if they represent attributes 

instead of entities, such as the start of a bridge. This is explained further in the transportation 

event model section below. No requirements are specified on how or where to place TranPoints, 

except as indicated above for TranSeg termini and that it is done consistently throughout the 

dataset. 

Figure 4 – Proper use of TranPoint class 

TranPoint is a subtype of TranFeature. TranPoints can therefore have a geometry and topology 

attribute and may have one or more attributes that are associated with the location where the 

point occurs. Geometry is restricted to be of type GM_Point and topology to be of type TP_Node. 

Both GM_Point and TP_Node are defined in ISO 19107. 

7.3.4 TranPath 

A TranSeg is used to represent a physical transportation real world entity and attributes about 

that entity. TranPath, as applied in the Rail, Roads, and Transit modal parts of the standard, shall 

represent how the TranSegs are organized and used such as administrative routes like US 50, or 

bus or train routes. Because it is a path through the physical transportation system, a TranPath is 

defined by a list of the one or more, whole or partial, TranSegs it uses. 

Figure 5 shows how TranPath extends TranFeature. It is an instance of the Feature class in the 

model shown in Figure 1. A TranPath can therefore have its own geometry. This optional 

TranPath geometry is of type GM_MultiCurve to allow for discontinuities in the path. The 

TranPath also inherits any geometry that may be defined by the TranSeg parts that comprise it. 

For example, the TranSeg geometries may be a more precise representation of the transportation 

feature, whereas the TranPath geometry may be a more generalized representation. Refer to 

each modal part for more information. 
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Figure 5 – TranPath model 
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7.3.5 Transportation system Listed below in Table 1 are the transportation objects and their attributes. 

Table 1 – Data dictionary for transportation system objects 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

1 TranFeature Transportation feature <<Feature>> 2 lastUpdateDate Timestamp indicating when the TranFeature object was last edited M 1 DateTime 3 Framework::Feature::identifier Feature identifier for the TranFeature M 1 <<DataType>> Framework::Identifier 4 Framework::Feature::geometry Geometric representation of the instantiated TranFeature entity O * <<Type>> GM_Object 5 Framework::Feature::metadata 

Structured or unstructured metadata as defined by the community of practice 

O 1 CharacterString 

6 Framework::Feature::topology Topological representation O * <<Interface>> TP_Object 7 Framework::Feature::attribute Producer-defined attribute for inclusion in transfer O * <<DataType>> Framework:: ExtendedAttribute 8 TranPath 

Linear, possibly discontinuous portion of the transportstion system that may be a collection of TranSeg instances 

<<Feature>> 

9 geometry Geometric representation of the instantiated TranPath entity O * <<Type>> GM_MultiCurve 10 routeNumber Public TranPath identifier M 1 CharacterString 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

11 topology Topological representation O * <<Type>> TP_Complex 12 Role name: segment Transportation segment feature used by the TranPath M * <<Abstract>> TranSeg 13 Role name: from Source TranPath in equivalency C/part of equivalency? * <<Feature>> TranPath 14 Role name: to Destination TranPath in equivalency C/part of equivalency? * <<Feature>> TranPath 15 TranPoint TranSeg terminus (start, end) <<Feature>> 16 geometry Geometric representation of the instantiated road point entity O * <<Type>> GM_Point 17 topology Topological representation O * <<Type>> TP_Node 18 Role name: startedSegment Segment that starts at the transportation point C/TranSeg starts at TranPoint? * <<Abstract>> TranSeg 19 Role name: endedSegment Segment that ends at the transportation point C/TranSeg ends at TranPoint? * <<Abstract>> TranSeg 20 Role name: from Source TranPoint in equivalency C/part of equivalency? * <<Feature>> TranPoint 21 Role name: to Destination TranPoint in equivalency C/part of equivalency? * <<Feature>> TranPoint 22 TranSeg Linear, continuous, non-branching portion of the transportation system <<Feature>> 23 status 

Status of segment entity; for example, proposed, under construction, open to traffic, abandoned, and so on 

M 1 CharacterString 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

24 fieldMeasure Length of segment, as determined in the field M 1 <<Type>> Measure 25 length 

Length of the TranSeg feature, which may differ from the field measured length due to differences in calculation 

M 1 <<Type>> Measure 

26 geometry Geometric representation of the instantiated segment entity O * <<Type>> GM_Curve 27 topology Topological representation O * <<Type>> TP_DirectedEdge 28 Role name: startPoint TranPoint corresponding to segment start O 1 <<Feature>> TranPoint 29 Role name: endPoint TranPoint corresponding to segment end O 1 <<Feature>> TranPoint 30 Role name: from Source TranSeg in equivalenye C/part of equivalency? * <<Abstract>> TranSeg 31 Role name: to Destination TranSeg in equivalency C/part of equivalency? * <<Abstract>> TranSeg 
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7.4 Transportation event model 

Events are the mechanism by which attributes or entities can be linearly located along either a 

TranSeg or a TranPath linear feature. As can be seen in Figure 6, transportation events can be 

either AttributeEvents or FeatureEvents. 

Figure 6 – Transportation event model (1) 

If an attribute value of a TranSeg or TranPath linear feature has a single, constant value along 

the entire length of the feature (for example, status and fieldMeasure), the attribute exists at the 

feature (TranSeg or TranPath) level and it is sufficient to specify this single value with the feature. 

If the value of the attribute can change along the length of the linear feature (for example, speed 

limit, number of lanes), the location where each change occurs must also be specified. To 

accomplish this, AttributeEvents are used. Each attribute event specifies a particular value for an 

attribute of a linear feature along with the location along that feature for which the value applies. 
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Figure 7 – Transportation event model (2) 

Similarly, TranFeatures other than TranSegs, TranPaths, and TranPoints can have attributes, 

each with a single, constant value. One of these attributes can be the geometry of the feature. 

For example, a street sign Transportation Feature can have a height attribute and a point 

geometry. This feature can also be linearly located along one or more TranSegs or TranPaths. 

Each such linear location is specified by a Feature Event. The Feature Event linearly locates any 

TranFeature along a TranSeg or TranPath. 

As shown in Figure 7, both AttributeEvent and FeatureEvent are subtyped into point and linear 

events. A point event occurs at a single position along a TranSeg or TranPath. This position is 

called an “at” position. Linear events apply to a length of the TranSeg or TranPath. This interval 

is defined by a “start” and an “end” position on the TranSeg or TranPath. The “at”, “start”, and 

“end” positions used to locate an event are specified using a linearly referenced position 

expression. This expression specifies the linear reference method used to perform the 

measurement, the linear feature (TranSeg or TranPath) being measured, the measurement along 

the TranSeg or TranPath, and optionally the measurement laterally offset to either side. 
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7.4.1 LinearAttributeEvent 

LinearAttributeEvents (see Figure 7) provide the means of specifying the value and location of a 

single segment or path attribute that applies only to part of the segment or path. The value of the 

segment or path attribute is specified as the attributeValue, inherited from AttributeEvent. The 

location interval along which the value applies is specified by a start and end position along the 

segment or path, using two linearly referenced position expressions. The name of the attribute is 

specified by the linearEventType attribute. For subtypes of LinearAttributeEvent, see 

subsequent, transportation mode-specific parts of this standard. An example of a 

LinearAttributeEvent is the speed limit of a road. “Speed limit” is the road attribute 

(linearEventType). A value of 55 MPH (attributeValue) might apply for only part of the road 

segment, delineated by start and end positions along the road segment. LinearAttributeEvents 

have no geometry of their own but instead inherit any geometry which may have been defined for 

the segment or path to which they apply. 

7.4.2 PointAttributeEvent 

PointAttributeEvents (see Figure 7) provide the means of specifying the value and location of a 

single segment or path attribute that has a particular value only at a single point along the 

segment or path. The value of the segment or path attribute is specified as the attributeValue, 

inherited from AttributeEvent. The point location is specified by an atPosition along the segment 

or path, using a linearly referenced position expression. The name of the attribute is specified by 

the pointEventType attribute. For subtypes of PointAttributeEvent, see subsequent, 

transportation mode-specific parts of this standard. An example of a PointAttributeEvent is a stop 

sign along a road. “Sign” is the road attribute (pointEventType). A value of “stop” (attributeValue) 

specifies the type of sign. The sign is located at a position along the road segment. The position 

expression allows the sign to be located at a position laterally offset from the center of the road. 

(If more information is needed about the sign, the sign shall instead be represented as a feature 

and then linearly located with a PointFeatureEvent. See section 7.4.4 below.) 

PointAttributeEvents can also be used to specify where something like a pedestrian cross walk 

crosses the segment or path. PointAttributeEvents have a linear location along a segment or 

path but have no explicit geospatial coordinate location of their own. This can be obtained from 

any geometry which may have been defined for the segment or path to which the 

PointAttributeEvent applies. 

7.4.3 LinearFeatureEvent 

A LinearFeatureEvent provides the means of specifying a linear location for a feature along a 

segment or path. All of the feature’s attributes, including optional geometry, are included with the 

feature itself. The LinearFeatureEvent is only attributed with the linear location of the feature 

along a segment or path, specified by a start and end position along the segment or path using 

two linearly referenced position expressions (see Figure 7). There are no restrictions on the type 

of feature being located. The feature can be linear, like guardrail. Guardrail attributes, like date 

installed or manufacturer are kept with the guardrail feature. The guardrail feature may not have 

geometry of its own, but instead rely on the geometry of the locating segment or path. Features 

with area geometries, like a county, are also supported by LinearFeatureEvents. In this case, the 

LinearFeatureEvent depicts what part of the segment or path is in the County feature. 

7.4.4 PointFeatureEvent 

A PointFeatureEvent provides the means of specifying a linear location for a feature along a 

segment or path. All of the feature’s attributes, including optional geometry, are included with the 

feature. The PointFeatureEvent is only attributed with the linear location of the feature along a 

segment or path, specified by a single atPosition along the segment or path using a single linearly 

referenced position expression (see Figure 7). There are no restrictions on the type of feature 

being located. The feature can have a point footprint, like a stop sign. Sign attributes, like date 

installed or height are kept with the sign feature. The sign feature may not have geometry of its 

own, but instead rely on the geometry of the locating segment or path. Features with linear 
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geometries, like a railroad, are also supported. In this case, the PointFeatureEvent depicts where 

the railroad crosses the segment or path. 
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7.4.5 Attributes for events Listed below in Table 2 are transportation event objects and their associated attributes. 

Table 2 – Data dictionary for transportation event objects 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

32 TranEvent 

Mechanism for locating an attribute value or feature along a transportation feature 

<<Abstract>> 

33 source Supplier of the event object M 1 CharacterString 34 Role name: locatingFeature Transportation feature to which event is referenced M 1 <<Union>> LocatingTranFeature 35 AttributeEvent Mechanism for locating an attribute value along a transportation feature <<Abstract>> 36 attributeValue Value of the attribute at the specified location M 1 CharacterString 37 LinearAttributeEvent 

Mechanism for locating an attribute value for an interval along a transportation feature 

<<DataType>> 

38 startPosition 

Starting location along the transportation feature for the attribute value 

M 1 <<Type>> LR_PositionExpression 

39 endPosition 

Ending location along the transportation feature for the attribute value 

M 1 <<Type>> LR_PositionExpression 

40 PointAttributeEvent 

Mechanism for locating an attribute value at a single point along a transportation feature 

<<DataType>> 

41 atPosition Point location along the 

transportation feature at which the 

M 1 <<Type>> LR_PositionExpression 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

attribute value applies 

42 FeatureEvent Mechanism for locating a feature along a transportation feature <<Abstract>> 43 Role name: linearlyLocatedFeature Feature that is located along the transportation feature M 1 <<Abstract>> Framework:: Feature 44 LinearFeatureEvent 

Mechanism for locating a feature along an interval along a transportation feature 

<<DataType>> 

45 startPosition Starting location along the transportation feature for the feature M 1 <<Type>> LR_PositionExpression 46 endPosition Ending location along the transportation feature for the feature M 1 <<Type>> LR_PositionExpression 47 PointFeatureEvent 

Mechanism for locating a feature at a single point along a transportation feature 

<<DataType>> 

48 atPosition 

Point location along the transportation feature at which the feature is located 

M 1 <<Type>> LR_PositionExpression 

49 LocatingTranFeature Transportation feature used to locate a transportation event <<Union>> 50 segment TranSeg used to locate a transportation event C/if path is not specified 1 <<Abstract>> TranSeg 51 path TranPath used to locate a transportation event C/if segment is not specified 1 <<Feature>> TranPath 52 Role name: event Transportation event located by the feature M * <<Abstract>> TranEvent 
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Part 7: Transportation Base 

Annex A (informative): Equivalencies

20

Annex A 

(informative) 

Equivalencies 

The central issue for the Transportation theme is how to equate disparate databases that 

represent the same real world features. For example, different databases may have different 

positional accuracies, different linear reference methods (LRMs), or different schemes for 

partitioning (segmenting) the transportation network. End users may have a variety of compelling 

business needs to distinguish each representation but also know that each is a representation of 

the same transportation system. “Equivalency” is the term given to the process of equating 

transportation segments or points from disparate databases. 

Assume that there are three segmentation schemes developed for a real road, as depicted in 

Figure A.1. All datasets include only RoadSegs. The basic difference between the two local 

RoadSeg datasets is the use of different intersections to base the segmentation; that is to say, to 

form RoadSeg termini. 

Figure A.1 – Sample datasets representing the same segment of road 

For simplicity, the only mandatory attributes of a RoadSeg are its identifier and length. The State 

DOT dataset includes a single RoadSeg with linear reference method (LRM) measures for the 

intersections (point events) and RoadSeg termini. To make it more interesting (and realistic), 

different resolutions for LRM measures are shown on the three datasets. Here are all the 

numbers: 

• The State DOT dataset states that the road is 21.09 miles long, is modeled as a single 

road segment (SR 47), and includes three intersection point events along its extent at 

distances of 5.37, 10.53, and 11.85 miles from the LRM origin 

• Local Dataset 1 states that the road is 111,566 feet long and consists of two RoadSeg 

features, one has the feature ID of 47101 and is 55,598 feet long, and the other has a 

feature ID of 47102 and a length of 55,968 feet 

• Local Dataset 2 states that the road is 21.2 miles long and consists of three segments, 

5347A at 5.5 miles in length, 5347B at 6.5 miles in length, and 5347C at 9.2 miles in 

length 

Local Dataset 1: 

• Because RoadSeg 47101 ends at a location equivalent to the second intersection point 

event at 10.53 miles along the 21.09 mile long State DOT RoadSeg, RoadSeg 47101 is 

equivalent to the first 49.93% of the State DOT RoadSeg (10.53/21.09) 

• RoadSeg 47102 is therefore equivalent to the last 50.07% of the State DOT RoadSeg 

((21.09-10.53)/21.09) 
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Annex A (informative): Equivalencies

21

Local Dataset 2: 

• Because RoadSeg 5347A ends at a location equivalent to the first intersection point 

event at 5.37 miles along the 21.09 mile long State DOT RoadSeg, RoadSeg 5347A is 

equivalent to the first 25.46% of the State DOT RoadSeg (5.37/21.09) 

• RoadSeg 5347B starts at a location equivalent to the first intersection point event at 5.37 

miles along the 21.09 mile long State DOT RoadSeg and ends at the third intersection 

point event at 11.85 miles along the State RoadSeg. RoadSeg 5347B is therefore 

equivalent to that part of the State DOT RoadSeg starting at 25.46% and ending at 

56.19% (11.85/21.09) 

• RoadSeg 5347C is therefore equivalent to the last 43.81% of the State DOT RoadSeg 

(100-56.19) 

With these equivalences, it is now possible to use linear interpolation to determine equivalent 

locations along the RoadSegs in these datasets. For example, a point 3.00 miles along 5347A 

would be 13.89% along the State DOT RoadSeg: (3.00 / 5.5) x 25.46%. This equates to only 

2.93 miles (13.89% of 21.09) along the State RoadSeg. This lower mileage is expected, since 

the State believes it is 5.37 miles to the first intersection whereas Local Dataset 2 believes it is 

5.5 miles. 

Note Two important points, first, this is exactly the same straight-line interpolation as used by dynamic 

segmentation. Second, the differences in LRM units and values between the datasets are inconsequential 

as the distances are computed in the separate LRM values and are consistent within each linear reference 

method.
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Part 7: Transportation Base 

Annex B (normative): Package: Linear reference systems

22

Annex B 

(normative) 

Package: Linear reference systems 

B.1 Semantics 

This annex is clause 6.6 from ISO 19133:2005, Geographic information – Location based 

services – Tracking and navigation. ”The package “Linear Reference Systems” supplies classes 

and types to the definition of linear reference systems. Linear reference systems are in wide use 

in transportation. They allow for the specification of positions along curvilinear features by using 

measured distances from known positions, usually represented by physical markers along the 

right-of-way of the transportation feature. The classes for this system and their relationships are 

depicted in Figure B.1. 

B.2 LR_PositionExpression 

B.2.1 Semantics 

The class “LR_PositionExpression” is used to describe position given by a measure value, a 

curvilinear element being measured, and the method of measurement. The UML for 

LR_PositionExpression is given in Figure B.2. 

B.2.2 Attribute: measure : Measure 

The attribute “measure” gives measure (usually a distance) of this position expression. 

LR_PositionExpression :: measure : Measure 

B.2.3 Role: LRM : LR_LinearReferenceMethod 

The role “LRM” gives the linear reference method used for this position expression. 

LR_PositionExpression :: LRM : LR_LinearReferenceMethod 
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Annex B (normative): Package: Linear reference systems

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LR_OffsetDirection

+ left

+ right

+ above

+ below

<<enumeration>>

LR_OffsetReference

+ centerline

+ edgeOfTravel

+ rightOfWay

+ curb

+ edgeOfBerm

+ sidewalkInside

+ sidewalkOutside

<<CodeList>>

LR_LinearReferenceMethod

+ name : CharacterString

+ type : CharacterString

+ units : UnitOfMeasure

+ offsetUnits : UnitOfMeasure

+ positiveOffsetDirection : LR_OffsetDirection = "right"

+ project(pt : GM_Point) : LR_PositionExpression

<<Type>>

LR_ReferenceMarker

+ name : CharacterString

+ type : CharacterString

+ position[0..1] : GM_Point

+ location[0..1] : LR_PositionExpression

<<Type>>

0..*

+marker

LR_Element

<<Type>>

1

0..*

+datumMarkers

{ordered}

LR_PositionExpression

+ measure : Measure

<<Type>>

1

+LRM

0..1 +referent

1

+referenceDomain

LR_OffsetExpression

+ offsetReference : LR_OffsetReference

+ offset[0..1] : Measure

<<Type>>

0..1 +offset

Figure B.1 – LRS classes 

B.2.4 Role: referent [0..1] : LR_ReferenceMarker 

The optional association role “referent” gives the marker or known position from which the 

measure is taken for the linear reference method used for this position expression. If the referent 

is absent, the measurement is made from the start of the LR_element. 

LR_PositionExpression :: referent [0..1]: LR_ReferenceMarker 

B.2.5 Role: referenceDomain : LR_Element 

The role “referenceDomain” gives the linear object upon which the measure is taken for the linear 

reference method used for this position expression. 

LR_PositionExpression :: referenceDomain : LR_Element 

B.2.6 Role: offset[0..1] : LR_OffsetExpression 

The optional association role “offset” gives perpendicular distance offset of this position 

expression. If the offset is absent, then the position is on the LR_element. 

LR_PositionExpression :: offset[0..1] : LR_OffsetExpression 
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Measure

(from Units of Measure)

<<Type>>

LR_LinearReferenceMethod

<<Type>>

LR_ReferenceMarker

<<Type>>

LR_Element

<<Type>>

LR_OffsetExpression

<<Type>>

LR_PositionExpression

+ measure : Measure

<<Type>>

1 +LRM

0..1 +referent +referenceDomain 1 +offset 0..1

Figure B.2 – LR_PositionExpression 

B.3 LR_LinearReferenceMethod 

B.3.1 Semantics 

The type “LR_LinearReferenceMethod” describes the manner in which measurements are made 

along (and optionally laterally offset from) a curvilinear element. The UML for 

LR_LinearReferenceMethod is given in Figure B.3. 

B.3.2 Attribute: name : CharacterString 

The attribute: “name” gives the name of this linear reference method. 

R_LinearReferenceMethod :: name : CharacterString 

B.3.3 Attribute: type : CharacterString 

The attribute: “type” gives the type of this linear reference method. 

LR_LinearReferenceMethod :: type : CharacterString 

B.3.4 Attribute: units : UnitOfMeasure 

The attribute: “units” gives the units of measure used for this linear reference method for 

measures along the base elements. 

R_LinearReferenceMethod :: units : UnitOfMeasure 

B.3.5 Attribute: offsetUnits : UnitOfMeasure 

The attribute: “offsetUnits” gives the units of measure used for this linear reference method for 

measures perpendicular to the base elements. 

R_LinearReferenceMethod :: offsetUnits : UnitOfMeasure 

B.3.6 Attribute: positiveOffsetDirection : LR_OffsetDirection = "right" 

The attribute: “positiveOffsetDirection” gives the direction used as positive for this linear reference 

method for measures perpendicular to the base elements. The default value is right for positive, 

left for negative. 
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Part 7: Transportation Base 

Annex B (normative): Package: Linear reference systems

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R_LinearReferenceMethod :: positiveOffsetDirection : LR_OffsetDirection = "right” 

B.3.7 Role: marker[1..*] : LR_ReferenceMarker 

The association role “marker” aggregates all reference markers used by the linear reference 

methods. Normally, this will be grouped by linear element. 

R_LinearReferenceMethod :: marker[0..*] : LR_ReferenceMarker 

CharacterString

(from Text)

<<Type>>

UnitOfMeasure

(from Units of Measure)

<<Type>>

LR_OffsetDirection

+ left

+ right

+ above

+ below

<<enumeration>>

LR_Element

<<Type>>

LR_ReferenceMarker

<<Type>>

LR_LinearReferenceMethod

+ name : CharacterString

+ type : CharacterString

+ units : UnitOfMeasure

+ offsetUnits : UnitOfMeasure

+ positiveOffsetDirection : LR_OffsetDirection = "right"

+ project(pt : GM_Point) : LR_PositionExpression

<<Type>>

+marker 0..* +referenceElement 1..*

Figure B.3 – LR_LinearReferenceMethod 

B.3.8 Role: referenceElement[1..*] : LR_Element 

The role “referenceElement” aggregates all the linear elements along which this method is 

supported. 

R_LinearReferenceMethod :: referenceElement[1..*] : LR_Element 

B.3.9 Operation: project 

The operation “project” will find the measure of the point on a base element closest to the given 

point, and then express the point as a position expression for the linear reference method. If the 

point is precisely on one of the linear elements, then the offset will be zero there is no offset 

expression. 

R_LinearReferenceMethod :: project(GM_Point pt) : LR_PositionExpression 

B.4 LR_OffsetDirection 

The enumeration “LR_OffsetDirection” gives the four options for offset measure. The values “left” 

and “right” are the ones most commonly used. These offset directions are as viewed from above 

the linear element facing in the direction of increasing measure. If measures for above or below 

the pavement are needed such as for clearance measures, the vertical options are “above” and 

“below”. The UML for LR_OffsetDirection is given in Figure B.4. 
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Part 7: Transportation Base 

Annex B (normative): Package: Linear reference systems

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LR_OffsetDirection

+ left

+ right

+ above

+ below

<<enumeration>>

Figure B.4 – LR_OffsetDirection 

B.5 LR_ReferenceMarker 

B.5.1 Semantics 

The type “LR_ReferenceMarker” is used to describe reference markers used in linear reference 

systems. At least one of the attributes “position” or “location” shall be given. If both are given 

they shall refer to the same physical location. The UML for LR_ReferenceMarker is given in 

Figure B.5. 

B.5.2 Attribute: name : CharacterString 

The attribute “name” is the identifier used for this marker. 

R_ReferenceMarker :: name : CharacterString 

B.5.3 Attribute: type : CharacterString 

The attribute “type” is the type of this marker. 

R_ReferenceMarker :: type : CharacterString 

B.5.4 Attribute: position[0..1] : GM_Point 

The optional attribute “position” is the position of this for this marker, given in some coordinate 

system. If this attribute is not given, then the “location” shall be given. 

R_ReferenceMarker :: position[0..1] : GM_Point 

B.5.5 Attribute: location[0..1] : LR_PositionExpression 

The optional attribute “location” is the location of this marker given as a linearly referenced 

measure along and from the start of the underlying linear element. 

R_ReferenceMarker :: location[0..1] : LR_PositionExpression 

LR_ReferenceMarker

+ name : CharacterString

+ type : CharacterString

+ position[0..1] : GM_Point

+ location[0..1] : LR_PositionExpression

<<Type>>

CharacterString

(from Text)

<<Type>>

GM_Point

(from Geometric pri mitive)

<<Type>>

LR_PositionExpression

<<Type>>

Figure B.5 – LR_ReferenceMarker 
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Part 7: Transportation Base 

Annex B (normative): Package: Linear reference systems

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B.6 LR_Feature 

The type “LR_Feature” is a behavioral description of features used as base elements in a linear 

reference method. This is the most common approach used for LRSs. The UML for LR_Feature

is given in Figure B.6. 

LR_Feature

<<Type>>

LR_Element

<<Type>> FD_Feature

(from Fea tu re Data Mode l)

<<Type>>

Figure B.6 – LR_Feature 

B.7 LR_Element 

B.7.1 Semantics 

The type “LR_Element” describes the underlying curvilinear elements upon which the measures 

in the linear reference system are taken. The UML for LR_Element is given in Figure B.7. 

B.7.2 Role: datumMarkers[1..*] : LR_ReferenceMarker 

The ordered association role “datumMarkers” aggregates the markers along this element. The 

ordering of the markers is consistent with the order in which the markers would be found in 

traversing the LR_Element from beginning to end (that is to say, in increasing order of distance 

from the “zero marker” the beginning of the element). 

R_Element :: datumMarkers[1..*] : LR_ReferenceMarker {ordered} 

LR_ReferenceMarker

<<Type>> LR_Element

<<Type>>

0..*

+datumMarkers 1

{ordered}

LR_Feature

<<Type>>

Figure B.7 – LR_Element 
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Annex B (normative): Package: Linear reference systems

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B.8 LR_OffsetReference 

The code list “LR_OffsetReference” enumerates the offset reference types used for this linear 

reference method, see Figure B.8. The initial value domain included: 

1) "centerline" center of the structure of the highway, or reference line for the highway 

2) "edgeOfTravel" outside edge of all travel lanes 

3) “edgeOfPavement” outside edge of travel-lane quality paved surface 

4) "rightOfWay" edge of the legal right of way 

5) "curbFace" side of curb towards travel lanes (the roadway must be curbed for this to 

be used) 

6) "curbBack" side of curb away from travel lanes (the roadway must be curbed for this 

to be used) 

7) “edgeOfShoulder” outside edge of all hardened surfaces (paved or gravel) 

8) ”edgeOfBerm" outside edge of leveled land for the road structure 

9) ”walkwayInside" sidewalk edge closest to travel lanes (a walkway must exist for 

this to be used) 

10) ”walkwayOutside” sidewalk edge furthest from travel lanes (a walkway must exist 

for this to be used) 

B.9 LR_OffsetExpression 

B.9.1 Semantics 

The type “LR_OffsetExpression” is used to describe the offset for a position described using a 

linear reference method. The UML for LR_OffsetExpression is given in Figure B.8. 

B.9.2 Attribute: offsetReference : LR_OffsetReference 

The attribute “offsetReference” indicates the base line for the offset measure. 

R_OffsetExpression :: offsetReference : LR_OffsetReference 

B.9.3 Attribute: offset[0..1] : Number 

The optional attribute “offset” is the measure of the offset of the position expression. A missing 

value is to be interpreted as being located at the offset reference. 

R_OffsetExpression :: offset[0..1] : Measure 

LR_OffsetExpression

+ offsetReference : LR_OffsetReference

+ offset[0..1] : Measure

<<Type>>

LR_OffsetReference

+ centerline

+ edgeOfTravel

+ rightOfWay

+ curb

+ edgeOfBerm

+ sidewalkInside

+ sidewalkOutside

<<CodeList>>

Measure

(from Units of Measure)

<<Type>>

Figure B.8 – LR_OffsetExpression 
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Geographic Information Framework Data Content Standard 

Part 7: Transportation Base 

Annex C (informative): Bibliography

29

Annex C 

(informative) 

Bibliography 

The following documents contain provisions that are relevant to two or more transportation parts 

of the Framework Data Content Standard. References applicable to a single transportation part 

are reported in the respective part. Annex D of the Base Document (Part 0) lists informative 

references applicable to two or more parts of the standard, including the transportation parts. For 

dated references, only the edition cited applies. For undated references, the latest edition of the 

referenced document applies. 

ANSI and ISO standards may be purchased through the ANSI eStandards Store at 

http://webstore.ansi.org/ansidocstore/default.asp, accessed October 2006. 

ISO 14825:2004, Intelligent transport systems – Geographic data files (GDF) – Overall data 

specifications 

NCHRP Project 20-27 (2), 1997, A generic data model for linear referencing systems, National 

Cooperative Research Program of the Transportation Research Board