Where to lookup the units associated with EPSG code?

Question

I'm trying to find a source of information with the default units (meters, ft, ftUS) associated with an EPSG code. I'm currently using https://spatialreference.org/ and fetching URLs like this:

http://spatialreference.org/ref/epsg/2284/proj4/

And then looking at the to_meter field to see if it's ft ftUs or m.

The problem is that the site seems to be incomplete for example they don't have EPSG:6505

http://spatialreference.org/ref/epsg/6505/proj4/

Answer 1

The official resource for EPSG codes is http://www.epsg.org/. You can either download the whole dataset or use the online registry http://www.epsg-registry.org/ that is unfortunately not very user friendly. All other sites are still only more or less accurate copies

The definition of EPSG:6505 captured from http://www.epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::6505

PROJCRS["NAD83(2011) / Minnesota South (ftUS)",
  BASEGEODCRS["NAD83(2011)",
    DATUM["NAD83 (National Spatial Reference System 2011)",
      ELLIPSOID["GRS 1980",6378137,298.257222101,LENGTHUNIT["metre",1.0]]]],
  CONVERSION["SPCS83 Minnesota South zone (US Survey feet)",
    METHOD["Lambert Conic Conformal (2SP)",ID["EPSG",9802]],
    PARAMETER["Latitude of false origin",43,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Longitude of false origin",-94,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Latitude of 1st standard parallel",45.216666666667,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Latitude of 2nd standard parallel",43.783333333333,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Easting at false origin",2624666.6667,LENGTHUNIT["US survey foot",0.304800609601]],
    PARAMETER["Northing at false origin",328083.3333,LENGTHUNIT["US survey foot",0.304800609601]]],
  CS[cartesian,2],
    AXIS["easting (X)",east,ORDER[1]],
    AXIS["northing (Y)",north,ORDER[2]],
    LENGTHUNIT["US survey foot",0.304800609601],
  ID["EPSG",6505]]

Answer 2

Two sources other than SpatialReference.org to find this information:

• http://epsg.io (e.g. http://epsg.io/6505) -- Probably the better option. Can include .proj4 at the end e.g. http://epsg.io/6505.proj4 for the Proj4 representation.)
• http://www.epsg-registry.org/ (requires a form completion)

Answer 3

If you have a modern version of PROJ since version 6.0, you can use projinfo from a local console, e.g.:

$ projinfo -o PROJ EPSG:6505
PROJ.4 string:
+proj=lcc +lat_0=43 +lon_0=-94 +lat_1=45.2166666666667 +lat_2=43.7833333333333 +x_0=800000.00001016 +y_0=99999.99998984 +ellps=GRS80 +units=us-ft +no_defs +type=crs

Another output format is PROJJSON if you'd prefer JSON.

An alternative Python interface via pyproj could also be used to extract the length units for each axis:

from pyproj import CRS

crs = CRS.from_epsg(6505)
print({ai.unit_name for ai in crs.axis_info})
# {'US survey foot'}

crs = CRS.from_epsg(4326)
print({ai.unit_name for ai in crs.axis_info})
# {'degree'}

# Be aware some CRSs have different units for each axis:
crs = CRS.from_epsg(4979)
print({idx: ai.unit_name for idx, ai in enumerate(crs.axis_info)})
# {0: 'degree', 1: 'degree', 2: 'metre'}