The SRTM tiles are DEM data divided in to one degree blocks for the surface of the earth. The data is divided into two resolutions, one at 3 arc seconds (90m) and one at 30 arc seconds (900m). 80% of the earths surface is covered for all of the area between 60 degrees N and 53 degrees S. SRTM data is in WGS84 datum and the elevation units are in metres. Digital Elevation Data for creating contours and other spatial analysis. World DEM data.