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If I load a polygon layer and make a new column, how do I fill that column with the 1) area of each polygon and another column with 2) the length of the perimeter of each polygon?

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2 Answers

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Open field calculator, select the new column and type the following expression

  • For area: $area
  • For perimeter: $perimeter

Make sure your layer is in a projected coordinate system (not lat/long ) and in correct units. ( i.e. if your layer's projection has 'meters' as units, your area will be square meters )

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Are there other functions that begin with $? – HealthMaps Jul 24 '12 at 4:58
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Many actually, you'll see them in the field calculator. in QGIS 1.8, it's nicely organized under 'function list' in field calculator – spatialthoughts Jul 24 '12 at 5:49
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You also can use fTools: Vector menu -> Geometry Tools -> Export/Add geometry columns

It updates your layer automatically by adding AREA and PERIMETER columns.

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