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I'd like to create custom buffers in QGIS. Each buffer will surround a point. The buffers don't overlap. And each buffer has to have two constants:

  1. There is a 50m radius space around the point which is within the buffer.

  2. The buffer as a whole covers 10 acres.

The shape of the buffer will vary from buffer to buffer, so this detail is immaterial. What's important is, the buffers cover ten acres, including the 50m.

buffer images

The above illustration is an example of what I'd want the polygons to look like, they can be of any shape in the world - so long as each one covers, in total, 10 acres.

Eddie Arni
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  • A circular buffer with a radius of ~113 m would solve the problem as currently stated, but I suspect that's not what you want. Can you add some more information about what you want the additional polygon to look like? – csk Oct 15 '18 at 20:05
  • The above illustration is what I'd want the polygon to look like, it can be of any shape in the world - I'd be buffering out an area of forest around a tree with an endangered species nest in it's canopy, so the buffer has to avoid riparian areas, etc. – Eddie Arni Oct 15 '18 at 20:44
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    Your question is not nearly detailed enough. It's clear that you have specific requirements for this polygon, but you haven't fully explained what those requirements are. Please edit your question to include all of your requirements, otherwise anyone who tries to help is just guessing what you need. – csk Oct 17 '18 at 16:33
  • i guess I lack the vocabulary to be any clearer. There are only two requirements, and I've been as clear as I am capable in illustrating them: 1. they encompass a 50m buffer around a point. 2. They are a total of 10 acres. just as is explained in the above illustration. That's all I've got. – Eddie Arni Oct 22 '18 at 19:23

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One solution I've come across - thanks in part to this thread:

Calculating polygon areas in QGIS?

is to create an ordinary circular buffer around the point, then create a polygon shapefile layer the size and shape of the entire buffer, making sure it's larger than the 50m buffer around the point.

I was able to figure out the area of the larger buffered area by editing an "$area" field in the attribute table.

To make the larger buffer the right size - 40000m in this case - I just tweak the nodes of the shapefile then use the attribute table's field calculator to measure the new polygon as I work on it.

Here's a screenshot:

buffered image

Seems like a workable solution, though I'd like to find something with less steps.

Eddie Arni
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