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)?
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.
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