GDF Synopsis:

The GDF International Standard specifies the conceptual and logical data model and the exchange format for geographic data bases for Intelligent Transportation Systems (ITS) applications. It includes a specification of potential contents of such data bases (Features, Attributes and Relationships), a specification of how these contents shall be represented, and of how relevant information about the database itself can be specified (meta data).

The focus of this International Standard is on ITS applications and emphasizes road and road related information. ITS applications, however, also require information in addition to road and road related information.

The scope of GDF is beyond of a GIS data model and format, because GDF also regulates how data should be captured and how features and their relationships have to be defined. In the centre of the GDF data model resides the “Feature" which is a data base representation of a real world geographic object. Examples of real world geographic objects are roads or buildings. A Feature must belong to exactly one Feature Class and exactly one Feature Theme that are uniquely referenced by a Name and a Code. The different objects together making up a GDF are conceptually divided over three different levels. These levels are referred to as Level-0, Level-1 and Level-2. The Features are divided over level-1 and level-2 depending on whether they are simple (level-1) or complex (level-2). On Level-0 the basic graphical building blocks are defined. These basic building blocks are nodes (zero-dimensional), edges (one-dimensional) and faces (two-dimensional) or alternatively, dots, polylines and polygons. The feature category defines the type of representation of a feature, i.e. point, line, area, or complex. Objects represented by a point, line or area are called simple features, while complex features are composed by a group of simple features. Features have geometrical and also topologic information. Every feature has a specific feature class. Features can also share relationships. Relationships are used to express association between two or more feature like, for example, a prohibited manoeuvre from one road to another.
The most recent version of the GDF standard is ISO IS 14825. The next version is already under work and will for example include a XML delivery format.

The Geographic Data Files (GDF) are used to model road network data for navigation purposes.

 GDF is an international standard ISO/TC204 / CEN/TC 278

The original GDF version 3.0 is called the CEN standard. There are other variants of GDF, namely the TeleAtlas variant and the NavTech variant.

GDF 4.0 is the new version of GDF and is also released.

GDF is more than just a format. It is both a format & a schema and has rules that describe features, attributes & relationships.

GDF (Level 2) has complex features which are aggregations of other features, including other complex GDF features. The GDF structure allows user defined features, attributes & relationships.

GDF is self-defining, meaning meta data records define a GDF dataset’s structure.

GDF features are defined by the feature catalogs like:

• Roads & ferries (roads, junctions, parking areas, etc.)
• Administrative areas (cities, counties, countries, etc.)
• Named areas (postal areas, police district, etc.)
• Land cover and use (parks, airports, olive grove, etc.)
• Waterways
• Public transport
• Custom features

GDF attributes are defined by the attribute catalogs, like:

• street names
• house numbering
• time domains
• official language
• speed restrictions
• Custom Atributes

GDF topology is defined by the relationship catalogue :

• Prohibited maneuver
• Road element within administrative area
• Junction within administrative area
• Service at a junction
• Service along a road
• Stop point at a junction
• Custom relationships

Why Use GDF?

GDF is the widely accepted standard for road network data, particularly in Europe. It is fast gaining acceptance in US (ITS America) and is used for Intelligent Transportation Systems & Transport Telematics Applications.

GDF data models help answer the question "how do I get from here to there?", "where is …?" and "what will affect my travel?"

Compiled by Rakesh Rao, (from publicly downloadable Internet sources) Four Dimension Technologies, Bangalore, India