It is the Digital Elevation Model (DEM) map file which gives you the terrain modeling on the map screen. This allow you to see mountains and valleys instead of just a flat map view.

gmapdem.img, length 117907456
Header: 05.05.2010 10:05:42, DSKIMG, XOR 00, V 20.11, Ms 0
Mapset: Middle East DEM
data are of 28.01.2010

compare with yours and replace it if newer, gmapdem.img is the right name