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I have a bunch of UK polygons that are saved in my PostGIS database as WGS84 projection. I would like to calculate the area of these polygons using st_area.

According to this answer I can save these polygons in any equal-area projection to do this. Is it really true that I can use any equal-area projection? For example, if I save them in US National Atlas Equal area (SRID 2163) will that work?

In any case, is there a UK-focussed equal area projection that it would be most appropriate to use?

Community
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Richard
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  • The most common European Project (EU, EC Official) is Lambert azimuthal equal-area projection http://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection – Mapperz Dec 11 '14 at 14:55

3 Answers3

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You could calculate ST_Area on a geography type. Since you have data with WGS84 (SRID=4326), you can add a simple geography cast, e.g.

SELECT ST_Area(geom::geography)

which will return area in m² on a curved surface (sphereoid by default). This should be pretty close to the true surface area, without requiring any projection.

It would be interesting to see how the areas compares to data projected on EPSG:27700, which is a Transverse Mercator based national projection for the UK. More info on Wikipedia and The Ordnance Survey website.

Mike T
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I would prefer EPSG:3035. The ESRI codes might not be available on all platforms:

enter image description here

EPSG:2163 has a different lon_0 leading to a distortion of the map:

enter image description here

AndreJ
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  • Out of interest, how did you generate these images? – Richard Dec 12 '14 at 00:47
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    @Richard with QGIS. The coastline is from Natural Earth, and the grid from http://gis.stackexchange.com/questions/79680/qgis-os-grid-overlay – AndreJ Dec 12 '14 at 04:50
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Actually it would work as both are about ~~~~ the same latitiude but use the Euro version http://spatialreference.org/ref/esri/102013/

If you do not know- just GIS
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