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I am trying to calculate the areas of some polygons and i want to use the field calculator to measure the area. The result i got using this method is different from using the QGIS measurement tool. I am confused on which is correct. How can i do this correctly? Also is it possible to change the measurement unit of the field calculator to give result in meter square?

marked as duplicate by DPSSpatial, Chad Cooper, Paul, BradHards, radouxju Dec 9 '15 at 6:57

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If you calculate area with field calculator by $area expression, your result will depend on the projection of your shapefile. Ex. if your projection is EPSG:4326 you will get an area in degrees. If you want meters, you need to reproject your shapefile to another projection (metric).

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