Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

The GeoJSON spec says "The default CRS is a geographic coordinate reference system, using the WGS84 datum, and with longitude and latitude units of decimal degrees". It doesn't say seem to specify what the units of elevation/altitude/z are for points.

Is there a default unit of altitude for GeoJSON? If not, are there common conventions, or a way to specify units?

share|improve this question
    
Welcome. It is meters: wiki.geojson.org/RFC-001. Make a search for "z" and look at the second result. –  Andre Silva Jun 14 '13 at 0:02
    
Interesting that the specification doesn't give any 3d examples. –  Fezter Jun 14 '13 at 0:55
1  
Andre, RFC-001 says "This is historical material. This page has been superseded by RFC-2", and RFC-2 doesn't include that bit about z being in units of meters. –  John Wiseman Jun 14 '13 at 7:11
    
Not entirely surprising, GeoJSON is designed to be as simple as possible. Things like Z/M values and CRSes are useful, but much less commonly used and covered, though that is likely to change. –  scw Jun 14 '13 at 7:20

1 Answer 1

Meters above mean sea level, per the RFC-001 wiki specification doc:

WGS84 is implied and coordinates represent decimal degrees ordered as "longitude, latitude [,elevation]" with z expressed as metres above mean sea level per WGS84.

But, unspecified, per the later RFC-2 wiki specification doc:

The order of elements follows x, y, z order (or longitude, latitude, elevation for coordinates in decimal degrees)

...

A GeoJSON object without a member named "crs" contains geometries in a Geographic projection, in the WGS84 datum, with units in decimal degrees.

share|improve this answer
    
The edit on this answer makes it more confusing. The spec is already confusing enough. The answer here should be clear. –  groovecoder May 12 at 13:46

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.