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I need a square polygon to clip layers to, in QGIS, a perfect square perhaps. It needs to be a certain size. Anyone have any experience or any good ideas?

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  • Not sure what version this came out in but you may use the "CAD-like improved polygon capture" tool on the main editing toolbar. This will allow you to manually define each segment length to create a square.
    – artwork21
    Jul 27 '15 at 18:30
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    Look here : gis.stackexchange.com/questions/94728/…
    – Nahas
    Jul 27 '15 at 18:33
  • Welcome to gis.stackexchange! Please note that a good question on this site is expected to show some degree of research on your part, i.e. what you have tried and - if applicable - code so far. For more info, you can check our faq.
    – underdark
    Jul 27 '15 at 19:45
  • I did an hour or two of research, but time constraints meant I had less than a couple of hours to find the right tool as it needed to be discovered and installed and was not obvious from using help in QGIS. Anyhow there is a new answer so perhaps the collective state of GIS knowledge has advanced somewhat.
    – lewis
    Jul 27 '15 at 20:15
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  1. Create a custom CRS around the center of the desired square:
+proj=tmerc +lon_0=7 +lat_0=51 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +towgs84=0,0,0,0,0,0,0 +no_defs
  1. Create a textfile with the following content for a 10*10 km square:
Geom,
"POLYGON((-5000 -5000, -5000 5000, 5000 5000, 5000 -5000, -5000 -5000))"
  1. Add the file as delimited text

  2. Save the layer as a shapefile for further processing and delete the delimited text layer

  3. Densify the geometry with Vector -> Geometry tools -> Densify Geometries ...

  4. Save the layer to the CRS of the layer you want to clip

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  • Thanks, great answer, more firepower than I needed though. I'm sure another user will find it valuable, would make a great extension ; )
    – lewis
    Jul 27 '15 at 20:17

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