----------------------------Original message---------------------------- DEM stands for digital elevation model. Will be glad to send information sheets to you that explain DEM's and DLG's. DLG is digital line graph. Means all line data on a map other than the elevation info. Such as roads, streams, political bound. data and other info. Please give me your mailing address and we'll get this out shortly. John Shanton Earth Science Info. Cntr. US Geological Survey. Reston, Va.