Introducing the Shapefile Format

The Shapefile format is the exchange format for vector maps of the Environmental Systems Research Institute (ESRI). This format supports polygons, arcs, lines, and points. Each Shapefile contains one single theme, meaning that all the objects in the file are of the same type (either line, point, polygon, or another type of object). In the Shapefile format, a theme is described with four different files:

• A Shapefile (.shp) - Contains the geometry of the objects.

• A Dbase file (.dbf) - Contains the attributes of the objects. This file is optional.

• An index file (.shx) - Contains the indexes of the objects in the .shp file to facilitate access to data. This file is optional and is used to perform random access of geometries by the load-on-demand process.

• A spatial index file (.idx) - Contains tiling information. This file is Maps module specific and is used to perform load-on-demand on Shapefiles. This file is optional and is used to store tiling information for the load-on-demand process.

This format does not contain information concerning the coordinate system used to reference the position of the graphic objects. Objects in Shapefiles are often positioned within a geographic projection (IlvGeographicProjection), but this is far from being the rule.