Add to ORKGThis site offers a collection of United States Geological Survey (USGS) factsheets that introduce and explain a vast array of topics related to mapping. Each subject covers the history and development of that particular topic and includes any software or instruments that may be requried to utilize the information sources described. The topics covered on this site include: GIS, UTM, aerial photographs, map projections, map accuracy measurements, digital elevation models (DEM), satellite imagery, landcover mapping, hydrography, and numerous other components of maps. Information is available in several different formats (paper, html and pdf) and includes links back to other USGS services. Educational levels: General public, Graduate or profess...