What is a datum: ... http://www.geo.hunter.cuny.edu/~jochen/gtech201/lectures/lec6concepts/map%20coordinate%20systems/how%20to%20choose%20a%20projection.htm http://www.georeference.org/doc/guide_to_selecting_map_projections.htm http://msdn.microsoft.com/en-us/library/cc749633(v=sql.100).aspx
