DEM

http://www.google.com/imgres?hl=en&biw=1280&bih=662&tbm=isch&tbnid=6VulzfYc7tVVXM:&imgrefurl=http://www.alpix.com/3d/TerrainViewer/index.html&docid=qROOGXx2XNMGrM&imgurl=http://www.alpix.com/3d/TerrainViewer/TerrainViewer_DEM_and_Texture_1_s.jpg&w=529&h=267&ei=PSdJUNvLGYaY9QSpioGQBw&zoom=1&iact=hc&vpx=627&vpy=334&dur=3221&hovh=159&hovw=316&tx=233&ty=119&sig=104655054681110617605&page=1&tbnh=86&tbnw=170&start=0&ndsp=18&ved=1t:429,r:9,s:0,i:101

DEM

A digital elevation model is a digital model or 3D representation of a terrain's surface it is commonly used for a planet like Earth or the moon, or asteroid.