Resource files store information about the insertion point, scale, rotation, and density of an image. The Resource File Directory indicates where AutoCAD Map 3D searches for resource files for images you insert with Raster Extension (not those you add with Data Connect). Resource files have the same base name as the raster image with a .res extension.
When you insert an image, AutoCAD Map 3D looks for associated correlation sources, such as world files, resource files, and tab files. By default, AutoCAD Map 3D looks in the directory containing the image. However, for resource files, you can specify an additional location. The additional location applies only to resource files (.res). It does not apply to other correlation sources.