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I want to find the area of a set of shapes in QGIS. I can do this step(Vector>Geometery Tools>Export add Geometry Columns or alternatively add feature $area) but I need the output to be in square meters or alternatively square kilometres.

I'm struggling to ascertain what projection I should be using, (I've tried a range, WGS 84 EPSG:4326, WGS 84 /UT< zone 59S EPSG:32759 & NZGD2000 / New Zealand Transverse Mercator 200 EPSG:2193 but at no stage have I got values that are fit for purpose i.e. in square meters or kilometers). The area I'm interested in is on the SE coast of New Zealand or http://gpsinformation.net/utm-zones.gif 59 G on this map.

The other possibility is i'm using/have used the correct the projection but have not set up QGIS correctly to measure area. My process is to set the project CRS > resave the project with the new CRS > add layers > change layers to the selected crs.

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    Your choice of projection (EPSG:2193 or 32759) looks fine. Your Shapefile may still have different CRS such as geographical (latlong or long-lat) coordinates. To set it to desired projected (Xm/Ym) CRS, go to Layers Panel and right-click your Shapefile layer, Save as with your EPSG of choice and save as new filename. After that, you can start new QGIS project from scratch and Layer | Add Vector Layer to load your new Shapefile.
    – Kazuhito
    Nov 21, 2016 at 22:02
  • Thanks @Kazuhito, I got it to work using area calculations based on the project CRS. Applying the change in Layer CRS would enable me to use the default Layer CRS
    – Marine-Max
    Nov 21, 2016 at 22:48
  • Great to hear. :-) Would be nice if you can post your workflow as your answer.
    – Kazuhito
    Nov 21, 2016 at 23:28

1 Answer 1

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I was utilising the correct projection (obtained from http://gpsinformation.net/utm-zones.gif) but I needed the project CRS to be transformed to this projection for my mapping units to move to meters.

To transform the project CRS, as opposed to 'on the fly' reprojections, I saved a new project with my desired projection (WGS 84 /UTM zone 59S EPSG:32759).

Then followed the same workflow as before: Vector -> Geometry Tools -> Export add Geometry Columns.

The key point of difference:

enter image description here As suggested by Kazuhito reprojecting each layer by resaving them in the desired projection would enable the use of Layer CRS.

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  • Thanks for this nice and intuitive summary. Do you have a button or something to accept answer (which put green check-mark) for us to know this is closed? (Sorry I am a newbie and not sure where it is.)
    – Kazuhito
    Nov 23, 2016 at 9:38

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