In QGIS, how can I automate drawing a 100km x 100km square around a number of points, with the point being dead in the center?

I'd need to loop through all the points and create a polygon, but not sure what would be the automated way of doing so.

I was able to create buffers (circular) around the points, but now looking for a solution to convert those circles to squares -- something like the Envelope approach described here (but need it in QGIS): Creating square buffer around point feature using ArcGIS for Desktop?

  • 1
    what is the arrangement of points, are they in a square? – Willy Oct 4 '12 at 3:23
  • This depends strongly which area on the globe we are talking about. The polar and equatorial circumferences are different. And also: are your coordinates in degrees or cartesian? It should be fairly easy to calculate the bounding box with this information. – LarsVegas Oct 4 '12 at 9:52
  • The arrangement of points would be a square. 1km apart (or 500m apart). We're looking at North America only at this point, Canada specifically. – NikG Oct 4 '12 at 14:39

QGIS ships with OGR which has a method GetEnvelope():

# Returns the geometry's extent as a list (minx, maxx, miny, maxy)

You can easily use it from within your QGIS python console. If you want to convert those coordinates into a shape? Have a look at my answer to this question for some info on modules which will help you turning this list into a vector file. There you find also further details and some helpful links.

  • Thanks LarsVegas! Can you script the entire process in QGIS (or outside of QGIS)? – NikG Oct 5 '12 at 21:54

You could use the mmqgis plugin for QGIS, which provides some more user-friendly implementations and interfaces of some QGIS functions. It adds an additional menu button next to "Web" and "Processing" from where you can choose "Create > Create Buffers" to get this interface: the mmqgis interface You get the option to choose in what units you want to measure the radius, how many edges you want - choose 4 for a square - and how the buffer should be rotated. At least in my case I also needed to rotate it by 45 degrees, otherwise it would have had kind of a rhombus-orientation. I did not try out the attribute option.

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