[postgis-users] Computing area in km^2 from 4326 geometries

[Wood Brent]

--- Craig Miller <craig.miller at spatialminds.com> wrote:

> If the area function is returning square meters (depends on your projection)
> then just divide the answer by 4046.896 to get kilometers.
> 
>  
> 
> All area functions are squared by definition.
> 

But a sq degree varies in its area depending on latitude.

Transform your data using a SRID referring to an equal-area (or near enough to
equal area for your purposes) projection in the query for area:

area2d(transform(the_geom, <SRID>));

I have a custom polar projection I use (srid=200000, based on the SCAR ADD
projection) to do this for Antarctic regions stored in lat/long projection.


Cheers,

  Brent Wood