I am using QGIS to calculate the form (or shape) factor of polygons following what Louf and Barthelemy did here: http://rsif.royalsocietypublishing.org/content/11/101/20140924

The form factor is defined as the ratio between the area of the block and the area of the circumscribed circle (something similar as a convex hull but with a circular buffer). The form factor is always smaller than 1 (since it is the area of the polygon divided by the area of the circumscribed circle).

To do so, I have a shapefile with the polygons of each block in several cities. I calculated the area of each polygon, but I need to find a way to calculate the area of the circumscribed circle. At the same time, it would be very useful if the calculation method can be repeated through a script or a function in the field calculator so it can be repeated for a large dataset of city blocks.

  • Thanks Zimmi, I already thought about the possibility to use the centroid-most-distant-point line as the radius, but I don't know how to do it with QGIS. As a second option, you said that it would be rather easy to do it with PostGIS. How could I calculate it with PostGIS? – ccfarre Aug 19 '15 at 9:13
  • Did you ever figure it out through QGIS? I have the same question... – user112237 Jan 8 '18 at 15:19

Generally speaking, you need to find the distance from shape centroid to the most distant point on its boundary. That should be the radius of the circumscribed circle. It's rather easy to achieve with PostGIS, not sure about QGIS.

  • Could you show the solution for PostGIS? – Simbamangu Jan 9 '18 at 6:30

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