Geographic Data File

The Geographic Data File (GDF) is a standard used to describe and exchange road network-related data. Major map vendors such as TeleAtlas and NAVTEQ provide maps in GDF. The current GDF version 4.0 was published as an ISO standard in 2004 [1]. The conceptual data model of GDF identifies features, attributes and relationships which are defined in catalogues. The Feature Catalogue provides a definition of real world objects such as roads and buildings. The Attribute Catalogue defines a number of characteristics of features and possibility of relationships. The Relationship Catalogue describes relations between features that may be used, e.g. to indicate the right-of-way.

Figure 1: GDF levels

The GDF structure is organised in three levels which are illustrated in the above figure. In level 0 the fundamental geometrical and topological entities used are described. The entities are nodes (0-dimensional), edges or polylines (1-dimensional) and faces or polygons (2-dimensional). Level 1 adds the possibility to describe real world geographic objects with their characterising properties. The simple features in level 1 use the level 0 entities as their geometrical and topological representation and combine them with attributes and relationships. Examples for simple features are signposts, junctions, road elements, and address areas. The features can have attributes such as number of lanes and permissible direction of travel. Relationships between junctions and road elements can be used to model prohibited manoeuvres, e.g. those indicated by no left turn road signs. In level 2 simple features can be aggregated to describe complex features. Examples of complex features are roundabouts and highway junctions.

Depending on the kind of application different levels are used. As guidance through complex junctions requires a high level of detail, level 1 is required for route guidance applications. Level 2 is more appropriate for the calculation of shortest routes, as it is not required to consider the full complexity of how to traverse complex junctions and roundabouts.

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