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Let's have a list of SRS with proj4 definitions (e.g. spatial_ref_sys table). Is there a way to determine whether given SRS is geographic (lon,lat) or cartesian (x,y)?

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You can have a look at the proj4text string, and whether or not it has "+units=x" (usually m for metres) in there.

@dariapra's answer implies that all cartesian co-ordinate systems are projected using Universal Transverse Mercator, which isn't the case at all.

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If geographic, you will see that +proj=longlat; for instance, for SRS with EPSG code 4326:

+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs

If cartesian, you will see that +proj=utm, which stands for Universal Transverse Mercator coordinate system, which is cartesian; for instance, for SRS with EPSG code 23029:

+proj=utm +zone=29 +ellps=intl +units=m +no_defs

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Not if the data is in a non-utm projection – HeyOverThere Dec 11 '12 at 18:03
There is much more than "longlat" and "utm", e.g. tmerc, somerc, omerc, lcc, krovak, cass, sterea, aea, laea, stere, cea. Is "longlat" geographic SRS and the rest is cartesian? – romat2 Dec 11 '12 at 18:05

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