Coordinate Systems and Web Mapping

I have, as have many other GIS people, long struggled with the range of coordinate systems in use in different areas and locations. I am currently trying to cope with on the fly translations between British National Grid and WGS84 Web Mercator, the system of choice for Google Maps et al, for a Web GIS I am developing at work.

I came across this blog post explaining the history of the Web Mercator projection, which served to clear up a lot of my questions and confusion.

For my future reference use EPSG code 3857 and follow the these WKT parameters to correct for Google's assumption that the Earth is spherical:

PROJCS["Popular Visualisation CRS / Mercator", GEOGCS["Popular Visualisation CRS", DATUM["WGS84", SPHEROID["WGS84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7059"]], AUTHORITY["EPSG","6055"]], PRIMEM["Greenwich", 0, AUTHORITY["EPSG", "8901"]], UNIT["degree", 0.0174532925199433, AUTHORITY["EPSG", "9102"]], AXIS["E", EAST], AXIS["N", NORTH], AUTHORITY["EPSG","4055"]], PROJECTION["Mercator"], PARAMETER["semi_minor",6378137], PARAMETER["False_Easting", 0], PARAMETER["False_Northing", 0], PARAMETER["Central_Meridian", 0], PARAMETER["Latitude_of_origin", 0], UNIT["metre", 1, AUTHORITY["EPSG", "9001"]], AXIS["East", EAST], AXIS["North", NORTH], AUTHORITY["EPSG","3785"]]