1

I am calculating the area of my polygon and I have used WGS 84 UTM zone 32N to calculate the area (using geometry on the field calculator) of my polygon, and I obtained 745461 (without units).

How do I determine whether it is in square metres or square kilometres?

  • 2
    It will be in the units of your projection, in this case metres. – Ian Turton Jan 16 '16 at 17:22
  • 2
    745461 sq km would be an area larger than Chile or Zambia (though smaller than Turkey or Pakistan), while 745461 sq m would be one third the area of Monaco. But what's six orders of magnitude between friends? – Vince Jan 16 '16 at 20:49
2

I think we can over complicate this answer. It is meters, as UTM Zones are almost always going to use meters as their unit (exceptions are so rare as to not be worth a mention). If you suspect you are using something that is not meters it will say so.

Use this site as it is software independent if you must look it up.

http://spatialreference.org/

Then search for your system

http://spatialreference.org/ref/epsg/wgs-84-utm-zone-32n/html/

You will get this. Read down and look for the unit (the lower one).

PROJCS["WGS 84 / UTM zone 32N",

GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.01745329251994328,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4326"]],
UNIT["metre",1,
    AUTHORITY["EPSG","9001"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",9],
PARAMETER["scale_factor",0.9996],
PARAMETER["false_easting",500000],
PARAMETER["false_northing",0],
AUTHORITY["EPSG","32632"],
AXIS["Easting",EAST],
AXIS["Northing",NORTH]]
1

I think that you should check a few items:

  • check layer CRS
  • check project CRS (set automatically reprojection on the fly in: Settings > Options > CRS)
  • After open vector layer in QGIS use tool "identify Feautures" and select one feauture
  • In "Identify Results" dock window "expand all" and look for area units

Now you can use "Filed calcuator" or Vector > Geometry Tools > Export/Add Geometry columns - to compare results from "identify Feautures" and Field calculator.

  • Great propositions to all, it was really helpful. I think! I think Zoltan had a pretty practical way of verifying which is always valid for all CRS projections. – Mr Nk Jan 18 '16 at 2:08
  • @Zoltan and all the others, though it indicates m, the values are just too small to be real. 0.00169 for a road segment that shows 154m on Google Earth – Mr Nk Jan 21 '16 at 8:25
  • I am using WGS 84 / UTM 32N for 11.3 and 11.5 (W and E respectively) – Mr Nk Jan 21 '16 at 8:29
  • Can you share sample data ? – Artec Jan 21 '16 at 8:52
  • I can't upload data, and the JSON file is too long and exceeds the word limit – Mr Nk Jan 21 '16 at 12:12
1

The unit of the projection is used for area calculation, meter or decimal degree or feet. Check Settings/Options/Crs, see screenshot:

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.