[R-sig-Geo] How to identify unknown Coordinate systems?

[Barry Rowlingson]

On Tue, Jul 24, 2012 at 5:17 PM, Juan Tomas Sayago
<juantomas.sayago at gmail.com> wrote:
> Hello,
> I have data in an unknown projection  but I know where more or less where
> it is located, but I don't know from what to transform to what I want to
> use.

First of all it could be one of the global systems like UTM zones.
Find out which UTM zone you might expect it to be and see what the
coordinates are of the region you think it might be.

Also, make sure you haven't got a .prj file with your shapefile, or
that the CRS is hidden in some metadata file.

Or try looking up the geographical area here:

http://www.spatialreference.org/

 but you might have to be creative - searching for 'Great Britain'
doesnt find the British national grid system, but searching for
'British' does. That site is also good for checking UTM zones. Note
there's a lot of unofficial CRS in there.

 Another useful thing is to figure out if the coordinates are metres
or km or miles, feet and inches - how far apart are your points in the
coordinate system?

 If all that fails, if you have the location of some of your points in
a known coordinate system, you can probably work out the transform
yourself, but it's likely to be imprecise.

 Finally, try beating the person who gave you the data until they tell
you! Or being nice to them.

Barry