[OSM-dev] Units in the PostGIS database - what are they?

Nick Whitelegg nick at hogweed.org
Sat Mar 17 22:51:24 GMT 2007


I'm getting unexpected results with the units used in the PostGIS database - 
namely they don't seem to be metres. I would expect metres out of a Mercator 
projection.

Using Nick Burch's Where Am I? script, the distance between the villages of 
Fernhurst, West Sussex and Cheriton, Hampshire is 31km - they are on the same 
latitude. From my knowledge of the area, 31km or about 20 miles seems about 
right.

However, the difference between the eastings is greater than 31000 metres.

Cheriton has an easting of approximately -130000. Fernhurst has an easting of 
approximately -80000, giving a distance of 50km if the units were metres.... 
so clearly they are not. 

Also, Fernhurst is less than 80km west of the Greenwich Meridian - more like 
about 50-60km.

So... what units are the PostGIS coordinates in?

Thanks,
Nick




More information about the dev mailing list