For more, see Layer Management
In GeoSync, Layers are like features (hydrants, roads, parcels, etc) grouped together in seperate shapefiles.
Layer types include:
Shapefiles: Lines, Polygons, Points
AutoCAD DWG files
Drawing Exchange Files or DXF files
Microstation DGN files
Image files such as JPEGs, TIFFs, SIDs, etc...