ISO 17572-1:2015

INTERNATIONAL ISO
STANDARD 17572-1
Second edition
2015-01-15
Intelligent transport systems (ITS) —
Location referencing for geographic
databases —
Part 1:
General requirements and
conceptual model
Systèmes intelligents de transport (SIT) — Localisation pour bases de
données géographiques —
Partie 1: Exigences générales et modèle conceptuel
Reference number
©
ISO 2015
© ISO 2015
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
2.1 General terms . 1
3 Abbreviated terms . 7
4 Objectives and requirements for a location referencing method . 8
4.1 Objectives for an optimal location referencing method . 8
4.2 Requirements of the location referencing method . 9
5 Conceptual data model for location referencing methods .10
5.1 Role of conceptual model .10
5.2 Components of conceptual model .10
5.3 Description of the conceptual model .10
5.4 Location categories .11
5.5 Conceptual model of a road network.12
5.6 Conceptual model of area locations .13
Annex A (informative) Inventory of location referencing methods .15
Annex B (informative) Examples of location referencing methods in use (mapping to
conceptual data model for location referencing systems) .19
Annex C (informative) Description of UML expression elements .21
Annex D (informative) Comparison of definitions with TC 211 .23
Annex E (informative) TPEG2 UML modelling and physical format representations .25
Annex F (informative) TPEG2 location referencing container .27
Bibliography .28
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
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on the ISO list of patent declarations received (see www.iso.org/patents).
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 204, Intelligent transport systems.
This second edition cancels and replaces the first edition (ISO 17572-1:2008), which has been
technically revised.
ISO 17572 consists of the following parts, under the general title Intelligent transport systems (ITS) —
Location referencing for geographic databases:
— Part 1: General requirements and conceptual model
— Part 2: Pre-coded location references (pre-coded profile)
— Part 3: Dynamic location references (dynamic profile)
iv © ISO 2015 – All rights reserved

Introduction
A location reference (LR) is a unique identification of a geographic object. In a digital world, a real-world
geographic object can be represented by a feature in a geographic database. An example of a commonly
known location reference is a postal address of a house. Examples of object instances include a particular
exit ramp on a particular motorway, a road junction or a hotel. For efficiency reasons, location references
are often coded. This is especially significant if the location reference is used to define the location for
information about various objects between different systems. For intelligent transport systems (ITS),
many different types of real-world objects will be addressed. Amongst these, Location Referencing of
the road network, or components thereof, is a particular focus.
Communication of a location reference for specific geographic phenomena, corresponding to objects in
geographic databases, in a standard, unambiguous manner is a vital part of an integrated ITS system
in which different applications and sources of geographic data will be used. Location referencing
methods (LRM, methods of referencing object instances) differ by applications, by the data model used
to create the database or by the enforced object referencing imposed by the specific mapping system
used to create and store the database. A standard location referencing method allows for a common
and unambiguous identification of object instances representing the same geographic phenomena in
different geographic databases produced by different vendors, for varied applications and operating on
multiple hardware/software platforms. If ITS applications using digital map databases are to become
widespread, data reference across various applications and systems has to be possible. Information
prepared on one system, such as traffic messages, has to be interpretable by all receiving systems. A
standard method to refer to specific object instances is essential to achieving such objectives.
Japan, Korea, Australia, Canada, the US, and European ITS bodies are all supporting activities of Location
Referencing. Japan has developed a link specification for VICS. In Europe, the RDS-TMC traffic messaging
system has been developed. In addition, methods have been developed and refined in the EVIDENCE
and AGORA projects based on intersections identified by geographic coordinates and other intersection
descriptors. In the US, standards for Location Referencing have been developed to accommodate several
different location referencing methods.
This International Standard provides specifications for location referencing for ITS systems (although
other committees or standardization bodies can subsequently consider extending it to a more generic
context). In addition, this edition does not deal with public transport location referencing; this issue will
be dealt with in a later edition.
INTERNATIONAL STANDARD ISO 17572-1:2015(E)
Intelligent transport systems (ITS) — Location referencing
for geographic databases —
Part 1:
General requirements and conceptual model
1 Scope
This International Standard specifies location referencing methods (LRMs) that describe locations
in the context of geographic databases and will be used to locate transport-related phenomena in an
encoder system as well as in the decoder side. This International Standard defines what is meant by such
objects and describes the reference in detail, including whether or not components of the reference are
mandatory or optional, and their characteristics.
This International Standard specifies two different LRMs:
— pre-coded location references (pre-coded profile);
— dynamic location references (dynamic profile).
This International Standard does not define a physical format for implementing the LRM. However, the
requirements for physical formats are defined.
This International Standard does not define details of the Location Referencing System (LRS), i.e. how
the LRMs are to be implemented in software, hardware, or processes.
This part of ISO 17572 specifies the following general LRM-related sections:
— requirements of a location referencing method;
— conceptual data model for location referencing methods;
— inventory location referencing methods (see Annex A);
— examples of conceptual model use (see Annex B);
— description of selected UML elements (see Annex C);
— comparison of definitions with ISO/TC 211 (see Annex D);
— introduction to the TPEG physical format (see Annex E and Annex F).
It is consistent with other International Standards developed by ISO/TC 204 such as ISO 14825.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 General terms
NOTE As part of the general intent to harmonize this International Standard with the ISO/TC 211 family of
Geographic Information Systems International Standards, a comparison between terms and definitions of this
International Standard and of ISO/TC 211 International Standards is included in Annex D.
2.1.1
accuracy
measure of closeness of results of observations, computations, or estimates to the true values or the
values accepted as being true
2.1.2
area
two-dimensional, geographical region on the surface of the earth
Note 1 to entry: An area can be represented as an implicit area or an explicit area.
2.1.3
area location
two-dimensional location, representing a geographical region on the surface of the earth
2.1.4
attribute
characteristic property of an entity like a real-world feature
Note 1 to entry: It allows the identification of that feature by its attributes. An attribute has a defined type and contains
a value. Attributes can be either simple, i.e. consisting of one atomic value, or composite (see composite attribute).
2.1.5
coordinate
one of an ordered set of N numbers designating the position of a point in N-dimensional space
Note 1 to entry: N would be 1, 2, or 3.
2.1.6
complex intersection
intersection that consists at least of two or more junctions and one or more road elements
2.1.7
composite attribute
complex attribute
attribute consisting of two or more atomic values and/or attributes
2.1.8
datum
set of parameters and control points used to accurately define the three-dimensional shape of the earth
Note 1 to entry: The corresponding datum is the basis for a planar coordinate reference system.
2.1.9
descriptor
characteristic of a geographic object, usually stored in an attribute
EXAMPLE Road names or road numbers.
2.1.10
digital map database
structured set of digital and alphanumeric data portraying geographic locations and relationships of
spatial features
Note 1 to entry: Typically, such structures represent, but are not limited to, the digital form of hard copy maps.
For example, drawings can be imported into a Geographic Information System (GIS) and considered as a form
of digital map.
2.1.11
dynamic location reference
location reference generated on-the-fly based on geographic properties in a digital map database
2 © ISO 2015 – All rights reserved

2.1.12
explicit area
two-dimensional face on the surface of the earth, with a specified outline either being a simple geometric
figure or an irregular outline/polygon
2.1.13
face
two-dimensional element bounded by a closed sequence of edges not intersecting themselves
Note 1 to entry: The face is the atomic two-dimensional element.
2.1.14
implicit area
selection of road segments to be referenced belonging to a certain area (subnetwork)
Note 1 to entry: One implicit area can be built up of multiple subnetworks that are geographically connected.
2.1.15
international terrestrial reference frame
ITRF
realization of the ITRS
Note 1 to entry: The ITRF94 reference frame is consistent with WGS84 at the 5 cm level, and therefore is equivalent
to WGS84 for ITS applications.
2.1.16
international terrestrial reference system
ITRS
reference system for the earth derived from precise and accurate space geodesy measurements, not
restricted to GPS Doppler measurements, which is periodically tracked and revised by the international
earth rotation service
2.1.17
intersection
crossing and/or connection of two or more roads
Note 1 to entry: In GDF, an intersection is a level 2 representation of a junction which bounds a road or a ferry. It
is a complex feature, composed of one or more level 1 junctions, road elements, and enclosed traffic areas. The
definition is different from GDF because the location referencing system refers to real-world objects rather than
a database definition as defined in GDF.
Note 2 to entry: Crossings can be at-grade or grade-separated. Crossings that are grade-separated where no
connection between the road segments exists, are excluded from this definition.
2.1.18
junction
elementary element in the road network, connecting two or more road elements
Note 1 to entry: In GDF terms, it is a level 1 feature that bounds a road element or ferry connection. Junctions that
represent real crossings are at least trivalent (having three roads connected). A bivalent junction can only be
defined in case an attribute change occurs along the road (e.g. road name change). A junction is also coded at the
end of a dead-end road, to terminate it.
2.1.19
linear location
location that has a one-dimensional character
EXAMPLE A road segment.
2.1.20
link
edge
direct topological connection between two nodes that has a unique link ID in a given digital map database
Note 1 to entry: A link can contain additional intermediate coordinates (shape points) to better represent the
shape of curved features. A link can be directed or undirected.
2.1.21
link identifier
link ID
identifier that is uniquely assigned to a link
Note 1 to entry: A link identifier can be arbitrary or can be assigned by convention, to ensure that no multiple
occurrences of the same identifier will be used within one instance of a network or map database.
2.1.22
link location
location identifiable by a part of the road network database having one identifier or having a uniquely
identifiable combination of attributes throughout the continuous stretch
Note 1 to entry: One link location can consist of multiple links.
2.1.23
location
simple or compound geographic object to be referenced by a location reference
Note 1 to entry: A location is matched to database objects by location definitions, which specify what is meant
by a particular location. Without any explicit remark, it is meant to be a linear stretch in terms of topology in the
database network without any loops or discontinuities in between (linear location). It might also be only a point
in the network as a specialization of a linear stretch with length zero. In addition to that, a location can also be
a set of road elements representing an area. This area is expressible by a polygon or a list of linear locations. For
further description of different categories of locations, refer to 5.4.
2.1.24
location definition
actual delineation of exactly what is meant (and, therefore, what is not meant) by a particular location
within a specific database
Note 1 to entry: It is the precise location definition of the database object, or set of database objects, which is referenced.
EXAMPLE The GDF road elements that make up a particular instance of an ALERT-C location.
2.1.25
location reference
reference
label which is assigned to a location
Note 1 to entry: With a single LRM, one reference shall define unambiguously and exactly one location in the
location referencing system. The reference is the string of data which is passed between different implementations
of a location referencing system to identify the location.
2.1.26
location referencing method
LRM
methodology of assigning location references to locations
2.1.27
location referencing system
LRS
complete system by which location references are generated, according to a location referencing method,
and communicated, including standards, definitions, software, hardware, and databases
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2.1.28
matching
translating a location reference to a specific object in a given map database to attempt recognition of the
same identified object in both the sender’s and the receiver’s map database
Note 1 to entry: Matching is seen as a subsequent part to the method of decoding a location reference adhering to
the defined LRM.
2.1.29
node
zero-dimensional element that is a topological junction of two or more edges or an end point of an edge
Note 1 to entry: A node is created for topologically significant points, such as simple intersections of roads or
other linear features including boundaries but also for locations such as electric beacons, kilometre-posts, or
sensors detecting traffic flows, being significant points specified in a map.
2.1.30
node identifier
identifier assigned to a node
Note 1 to entry: A node identifier can be arbitrary, or can be assigned by convention, to ensure that multiple
occurrences of the same identifier will not occur within one network or within the universe of similar networks
or databases.
2.1.31
outlined area
explicit area with an outline defined by segments being either polylines or linear locations
2.1.32
point
zero-dimensional element that specifies geometric location
Note 1 to entry: One coordinate pair or triplet specifies the location.
2.1.33
point location
location that has a zero-dimensional character
EXAMPLE A simple crossing.
2.1.34
precision
exactness of the measurement of a data value or of the storage allocated to a measured data value
Note 1 to entry: Alternatively, the closeness of measurements of the same phenomenon repeated under exactly
the same conditions and using the same techniques.
2.1.35
pre-coded location reference
location reference using a unique identifier that is agreed upon in both sender and receiver system to
select a location from a set of pre-coded locations
2.1.36
quad tree
hierarchical data structure which, on a next lower level, subdivides a given area into four quadrants of
the same size where any level has knowledge of its four sublevels and its parent level
2.1.37
relationship
semantic or topological interrelation or dependency between locations in the LRS
Note 1 to entry: Relationships can exist between locations in the LRS. These relationships will generally be
structured to allow more sophisticated use of the location reference, such as a topological or hierarchical structure.
For example, a county location can be defined as an aggregate of several city locations or a long stretch of road can
be an aggregate of several smaller road segments. Referencing the county can be easier than referencing all the
cities which make up the county. This allows scalability and ease of use in the LRSs using the LRM.
2.1.38
resolution
smallest unit which can be represented fixing a limit to precision and accuracy
2.1.39
road
part of the road network which is generally considered as a whole and which can be addressed by a
single identification like a road name or road number throughout
Note 1 to entry: In general, it is a connection within the road network, with or without crossings, which functionally
can be considered as a unity. A road with multiple (associated) carriageways can be considered as one road. (Note
that, in the context of this part of ISO 17572, the term also covers the natural language term street).
Note 2 to entry: The subsequent parts of this International Standard intentionally do not make direct use of this
term because under different circumstances it might not be possible to define exactly where a road ends. For this
reason, reference will be made to artificial but more-precisely-definable road elements or road sections of the
road network.
2.1.40
road crossing
location where two or more roads connect or intersect
Note 1 to entry: A road crossing can be “simple”, corresponding to one junction, or “complex”, including internal
road elements and junctions.
2.1.41
road element
linear section of the road network which is designed for vehicular movement having a junction at each end
Note 1 to entry: It serves as the smallest unit of the road network at GDF level 1 that is independent.
2.1.42
road section
road segment that is bounded by two intersections and has the same attributes throughout
Note 1 to entry: Generally, the two intersections are different, only in some specific cases are the intersections the
same, e.g. a tear-drop street or slip roads inside of complex intersections.
2.1.43
road segment
part of a road, having its start and end along that road
Note 1 to entry: Important difference between a road section and road segment is that the segment does not
necessarily end at intersections.
2.1.44
shape point
intermediate coordinate pair to represent the shape of curved features
2.1.45
simple geometric area
explicit area with an outline defined by a simple geometric figure
6 © ISO 2015 – All rights reserved

2.1.46
simple object access protocol
SOAP
protocol providing a platform-independent way for applications to communicate with each other
over the Internet
Note 1 to entry: SOAP technology relies on XML to define the format of the information and then adds the necessary
HTTP headers to send it. Standardization is done within IETF: http://www.ietf.org/rfc.
2.1.47
subnetwork
plurality of road segments lying in geographical or topological conjunction to each other
2.1.48
synchronization markup language
SyncML
data synchronization protocol
Note 1 to entry: A data synchronization protocol defines the workflow for communication during a data
synchronization session when the mobile device is connected to the network. The protocol supports naming and
identification of records, common protocol commands to synchronize local and network data, and can support
identification and resolution of synchronization conflicts.
2.1.49
topology
properties of spatial configuration invariant under continuous transformation
Note 1 to entry: In a digital map database, this means the logical relationships among map features. It can be used
to characterize spatial relationships such as connectivity and adjacency.
2.1.50
world geodetic system of 1984
WGS84
earth-centred global reference frame, including an earth model, based on satellite and terrestrial data
Note 1 to entry: It contains primary parameters that define the shape, angular velocity, and the earth mass of an
earth ellipsoid, and secondary parameters that define a gravity model of the earth. Primary parameters are used
to derive latitude-longitude coordinates (horizontal datum).
3 Abbreviated terms
AGORA Implementation of Global Location Referencing Approach
(Name of a European project 2000–2002)
ALERT-C Advice and problem Location for European Road Traffic-Compact
CAD computer-aided design
EVIDENCE Extensive Validation of Identification Concepts in Europe
(Name of a European project 1998–1999)
GCId generic component identifier
GDF Geographic Data File
GIS Geographic Information System
GPS Global Positioning System
IETF Internet Engineering Task Force
ILOC intersection location
ITS intelligent transport systems
LR location referencing (or reference)
LRC location reference container
POI point of interest
RDS Radio Data System
TPEG Transport Protocol Expert Group
TMC Traffic Message Channel
TTI Traffic and Traveller Information
UML Unified Modelling Language
UTM Universal Transverse Mercator
VICS Vehicle Information and Communication System
NOTE This International Standard uses UML to express specific circumstances. As such, the graphical
elements are used to express specific constraints and structural relationships. A full definition can be found in
the UML standard ISO/IEC 19501. However, a short introduction of used elements is given in Annex C.
4 Objectives and requirements for a location referencing method
4.1 Objectives for an optimal location referencing method
ITS applications have different objectives regarding location referencing, which from their contradictory
nature, cannot be fulfilled completely. In theory, a best location referencing method would require every
LRS to have at a given time the same, completely accurate map and all locations would be identifiable
without any additional computational effort. Even though this is not achievable, the following goals
should guide the definition and optimization of a location referencing method. The circumstances of the
specific location referencing system can give different weight to the following goals.
The first goal therefore states that processing power in any case is a cost factor to be minimized.
O-1. The LRM should be simple enough to be implemented in a resource- and performance-
efficient way.
Secondly, location referencing implies at least two systems communicating with each other.
Communication also causes costs and therefore needs to be minimized.
O-2. The LRM should not unduly add to the volume of data to be transferred.
The aim to use the exact location, both in the sender and the receiver system, is the reason of referring
to it. In many cases, it will be up to the receiver to decode the location reference as well as possible. To
help the receiver to do so, it shall be implied that the sending system sends the location reference as
accurately as possible.
O-3. The LRM should provide location references with the highest accuracy possible.
8 © ISO 2015 – All rights reserved

4.2 Requirements of the location referencing method
In addition to the goals, some minimal requirements shall make the different location referencing
methods feasible for the foreseen categories of locations (see 5.4).
One of the most important data characteristics for ITS applications is spatial accuracy. Spatial accuracy
is an aspect of data quality and is described in GDF in the following way: The shape of a level 0 edge
including all positions on the segment as a whole shall not have any position that diverges from the real
shape more than an allowed error. Spatial data accuracy requirements for ITS vary according to the
application. This means not just categories of applications but how an application works operationally.
Some applications, notably those for advanced vehicle safety systems, would require very accurate data.
Even within a particular application, requirements for different levels of data accuracy might exist and
will be subject to change as applications and products evolve. The spatial data accuracy requirements
impact on the location referencing method chosen for an application.
One fundamental requirement across all methods is that, whichever method is used, use of that method
does not result in additional spatial location error beyond that already present in the data. However, for
the location referencing of area information, for example weather information or information specifying
a zone of environmental contamination, some positional error is permitted due to the imprecise
(“fuzzy”) nature of such information. The key requirement for such references is that they be made with
sufficient precision to allow the user to avoid the area or take other appropriate action. Specifically, it is
a requirement that:
R-1. An LRM and the process of its operation shall not introduce a supplementary position
error relative to that specified in the database from which the reference is generated. The location
reference should be conveyed with spatial and temporal accuracy sufficient to enable the vehicle or
user to identify the (spatial) extent of the location.
For certain locations, knowing the side of the road or block on which the location is found can be
very important to the user. For example, crossing a road to a location on the opposite side might not
be possible for vehicles or pedestrians in some road lane configurations without additional routing,
whereas turning into a location on the same side can be easily accomplished. Therefore, it is a particular
requirement that:
R-2. The LRM shall enable referencing of the relative spatial relationship of objects.
In addition to spatial accuracy requirements, location referencing methods have functional requirements
regarding topological relationships, for example that a point is on one side of an object or that many
points shall be ordered in a certain way along a road. For example, for locations referenced by positions
along a logical or physical route, the ordering of points shall be preserved by the reference. For location
referencing, the requirement is that:
R-3. The LRM shall not change the topological relationships within a set of point data by its
own action, limitation, or deficiency. For referencing by geographic coordinates, spatial relationships
between locations should not be confused by lack of precision or by any other attribute of the
referencing system or its operation.
This International Standard is foreseen to be used in a variety of location referencing systems. However,
the restriction to some specified categories of locations is understood as a first step of optimization of
the defined location referencing methods. For this, the following shall at least hold:
R-4. The definition of an LRM shall adhere to the common terminology and conceptual model
defined in this part of ISO 17572.
R-5. The LRM shall provide means to refer only to the categories of locations explicitly
defined by that LRM.
R-6. The LRM shall, in principle, allow addressing of every location on the road network.
Location referencing is an important technology for traffic telematics applications in particular and,
in general, for any location based service. It provides an understandable reference for a location about
which information needs to be provided. Understandable generally means machine-readable, i.e. the
location information (as well as the message content) can be understood by equipment that translates
the complete message to human understandable information e.g. position on a map or a descriptive way
to reach the location. Therefore:
R-7. The location reference shall be machine-readable.
5 Conceptual data model for location referencing methods
5.1 Role of conceptual model
The conceptual model provides a framework to describe and define an LRM in generic, conceptual terms. The
conceptual model is generally valid, i.e. not limited to the LRMs defined in this part of ISO 17572. Therefore,
examples of other LRMs are mentioned, to illustrate the underlying conceptual view. See also Annex B.
5.2 Components of conceptual model
All location referencing methods have some form of the following components. The detailed definitions
of the terms are provided in Clause 2.
Attributes
An attribute allows the LRS to process or evaluate the information about the location. Attributes
discriminate the reference in such a way that the receiver system can identify the location correctly.
Location
A location is a part of the road network that is intended to be identified. The sender system aims to refer
to it; the receiver system aims to find it in its map database.
Location definition
The location definition is the defined delineation in a digital map database of exactly what is meant.
The location definition in a sender system can be different from the one in a receiver system even if the
location is the same.
Reference
The reference is the label which is assigned to the location.
Relationship
Relationships to other locations in the LRS are also used to support the use of locations in an LRM.
NOTE Not all LRMs require relationships and attributes. For example, an LRS which uses arbitrary numbers
assigned to each location might never need to define how any of the locations relate to each other. However, in
an LRS which meets the requirements which have been identified (such as flexibility, extensibility, compactness,
etc.), relationships can be inherent in the referencing procedures. For example, pre-coded locations used in RDS-
TMC systems arbitrarily number locations, but since the referencing system allows the use of an “extent,” each
location can carry the definitions of which location is “before” and “after” it.
5.3 Description of the conceptual model
A reference is the label which is assigned to a location. In a single LRS, a reference shall be defined or
definable which unambiguously identifies each location in this LRS. A location is a simple or compound
geographic object, which is matched to database objects by location definitions, which specify what
is meant by the particular location. A location can aggregate different attributes, which allow for the
identification of the methods to process or evaluate the information about the location. Relationships
10 © ISO 2015 – All rights reserved

associate different locations, e.g. to allow more sophisticated use of the location reference, such as a
topological or hierarchical structure; they are intended to reflect the possibility of two or more locations
in a relationship, either ordered or unordered.
Figure 1 — Diagram of the conceptual model of an LRM
5.4 Location categories
Locations shall be categorized as point locations, linear locations, and area locations. These location
categories represent real world objects which can be described as follows:
— existing at a single position (point location);
— between two positions within intersections as road section (linear location, in terms of one or more
link locations);
— between two positions as road segment (linear location);
— consisting of two or more link locations (linear location);
— a selection of road segments belonging to a defined collection (subnetwork or collection of
subnetworks) (implicit area location);
— within the boundaries of a defined area (explicit area location).
Point locations can be described as existing at a single position. Point locations include, for example,
points of interest, public service facilities, commercial establishments, etc. Link locations are linear
objects bound by two point locations. Linear locations are two or more consecutive link locations,
bounded, therefore, by three or more consecutive point locations that define a connected linear stretch
in the road network. Implicit area locations are more than one linear location of a certain area put
together in one package. Explicit area locations are two-dimensional features such as governmental
administrative area, postal district, telephone exchange district, etc., or just defined outlines as faces at
a given place on the map.
Specific reference object instance classes within these categories include the following:
— general points (points that might or might not lie on a road network, including points where a road
crosses administrative boundaries or borders of map grid cells);
— points at nodes in a topological network representation of roads and their intersections;
— links defined by two consecutive intersections of roads (road sections);
— points along links bounded by intersections of roads;
— manoeuvres defined by two consecutive links (therefore, three intersections);
— areas defined by a sequence of points;
— areas defined by a sequence of link locations;
— areas defined by an origin point and attributes, such as the radius of a circle around the point or
offsets defining a bounding box.
Generally, important location categories for ITS databases are man-made structures like road crossings,
road sections or segments, as well as sequences of road sections necessary for describing manoeuvres.
Location categories can be arranged in class/type hierarchies to aid in decoding between dissimilar
receiver/sender systems.
5.5 Conceptual model of a road network
One purpose of location referencing is to refer to parts of the road network. The conceptual model
of the road network is, therefore, depicted in Figure 2 and described in this subclause to give a clear
understanding of the different terms and their relationships. This is especially needed because the
sophisticated definition of roads and intersections in GDF does not meet the requirements of a conceptual
model for location referencing.
In general the road network consists of roads. A road is generally represented by a name (or number)
throughout as a whole and consists of a set of road sections. On a road a tremendous (but countable)
number of road segments can be defined (and referenced). A road section consists of nodes and edges,
is bounded by intersections, and can have intermediate intersections (where the road name does not
change). An intersection is a connection or crossing of roads. The simplest intersection consists of just
one node (i.e. junction). If an intersection has two or more nodes and one or more edges, it is considered
to be a complex intersection.
12 © ISO 2015 – All rights reserved

Figure 2 — Conceptual model for the physical road network
5.6 Conceptual model of area locations
An area is considered to be a two-dimensional, geographical region bounded on the surface of the earth.
Area locations have specific constraints on location referencing due to requirements of the application.
The different requirements of the applications determine if the full geographical figure shall be
mentioned or a defined number of roads inside this region. To enable an LRM handling and defining rules
for explicit and implicit area types, the conceptual model defines terms for it and describes conceptually
their containment.
In one case, it might be feasible to define the area by a geometric figure (explicitly). In other cases, it
might be necessary to select a list of road elements spanning an area (implicitly).
An implicit area consists of one or more subnetwork locations which each consist of at least two road
segments being aggregated to the subnetwork. The explicit area specifies a part of the earth surface
being the area, by means of a geometric (regular) function, defined as region; meanwhile, an area with a
shape freely defining the shape of it is called outline. Both of the area types have at least one referenced
connection to the surface allowing the decoding system to precisely position the given area.
Subnetwork
Figure 3 — Conceptual model of areas
14 © ISO 2015 – All rights reserved

Annex A
(informative)
Inventory of location referencing methods
A.1 General
There are two essentially different ways of referencing road locations: with reference to attributes of
the road network itself, including linear distances or street addresses, or with reference to a regular
or irregular division of space which exists independent of the representation of the road network. The
former kind of reference is sometimes called an indirect reference. The latter kind involves coordinate
systems, for example US UTM coordinates or geographic latitude/longitude coordinates.
Some indirect referencing methods stress the topology of networks (for example, link ID and Linear
Referencing), and some stress the attributes of the features that comprise the network (for example,
cross-street offset matching and street addresses). Geographic coordinates express location directly
in terms of the geodetic reference framework itself; they are simply measurements on the framework
(e.g. longitude/latitude) or as quantized, regular subdivisions (e.g. quad trees). Figure A.1 illustrates
indirect (specifically, the link ID method) and coordinate referencing methods (specifically, the method
of geographic coordinates).
Figure A.1 — Indirect (link ID) vs. ge
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