Thank you for the fast reply.
I would have thought that longitude / latitude were simple units for a map.
My map server uses the same units as used in the map "shape" files, I obtained those from http://download.geofabrik.de/osm/europe/.
If I knew what units GMaps expects I could try to find more suitable shape files or convert the units.
So the original question still stands, what units is GMaps using or do you know of a source of shape file using the correct units?
James