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First, I am using QGIS 2.8.2.

I have GPS waypoints and satellite imagery and am trying to draw polygons. This is easy enough, but I need to make sure each polygon is 1ha exactly. Is there a way to create polygons using the given area first?

I am creating polygons to delineate areas for community members' rights to do agro-forestry, so the final area of each polygon needs to be exact to be fair to everyone. The shape of the polygons will be rectangles, but not necessarily all right angles due to the terrain.

  • Does the waypoints represent the corners of the polygons? – user16032 Feb 15 '16 at 6:51
  • Due to fieldwork constraints, I could only get the general location of where the polygon would go. So, I am planning on just validating the area using the satellite imagery. – enathaniel Feb 15 '16 at 8:10
  • If the plots were rectangles (don't they always have just right angles en.wikipedia.org/wiki/Rectangle?) it should not be so hard for someone who knows python to make a special tool. It might create first a 100x100 m square and make it wider if users moves a border and makes the box lower. The mathematics is easy. Besides that you would need tools for rotating and moving. – user30184 Feb 15 '16 at 9:21
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I don't think there will be you can have non-rectangular shapes kept at a constant size, if you move one corner what decides how the others are moved to adjust the size? I would say just create one feature the right size and copy it around as required but since some will be irregular (not right angles) I suggest setting a label with the area so you can adjust the corners to get the size right and you could set a style so that the fill colour goes green when the size is correct.

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I haven't tried it, but there is the CalcArea plugin, which apparently "calculates the area of a polygon while it's being created or edited".

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