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I have a CSV file with various data in 1 degree wide by 0.5 degree high rectangles, for which I have the N,S,E,W, & centroid lat/longs, i.e. every bit of spatial data required. I'm trying to convert this into a polygon grid, so that I can display the associated data in the variety of ways that raster doesn't do nearly as well (for ref: I have successfully converted to raster using this method (point > shape > raster)).

Other Q&As recommend points2one plugin, however this results in a big mess of triangles; in addition, no matter how I import the csv, qgis will only display one point per cell, either the centroid (manually selecting centroid lat/long) or the NE corner (default, qgis picks up the NORTH & EAST field names).

I've just successfully done this using WKT, creating a formula in excel to generate the polygons from the NESW coordinates, which seems like the best way so far.

My question is: is there a better way of doing this natively in QGis? It feels like the software has all the info available to be able to do this with one or two clicks - am I just missing it?

Thanks!

p.s. if anyone reads this & is in the same boat, my formula was: ="POLYGON (("&E2&" "&D2&", "&E2&" "&F2&", "&G2&" "&F2&", "&G2&" "&D2&", "&E2&" "&D2&"))" with S/W/N/E in columns D/E/F/G respectively, and the formula in H. Remember to copy * paste back over the output as values before you save.

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You could try Vector / Geometry Tools / Voronoi polygons (using the point layer from your CSV file as input). Here is an example of the result based on a regular point grid:

enter image description here

  • An interesting approach; quick, but creates problems at the boundaries since it doesn't use the NESW data: see LINK for screengrab, with bottom-top layer order being: Official ICES rectangles with codes (that seem to to go the top layer for some reason), Europe map shape, voronoi polygons in semi-transparent mauve, the yellow centroids that produced the voronois. – dez93_2000 Sep 18 '13 at 15:55
  • Maybe it would help to add more points around your study area. I used a rectangle completely filled with regularly spaced points. The result consisted only of squares. You can delete the rectangles you don't need afterwards. – Sake Sep 18 '13 at 16:53
  • True indeed, but if you're going to that trouble you might as well use WKT, or put the work in to make points2one work properly. Not trying to be dismissive, just putting into context. – dez93_2000 Sep 18 '13 at 21:01

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