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I wanted a proportional symbols map of a quantitative variable. Following this question Proportional Symbol Formatting I tried with centroid fill and changing the size of the marker. Nevertheless this what I get using the 10m_admin_0_map_units layer from natural earth data:

enter image description here

As I understand each polygon should have just one marker, nevertheless they have more than one marker. I wonder if I am doing something wrong. I tried this solution since you can only work with color for the symbology method. There is no size option for polygons. I am working with Qgis 2.14.

  • You might want to dissolve the features based on a COUNTY attribute in the 10m_admin_0_map_units table - does such an attribute exist? – DPSSpatial Jun 21 '16 at 18:44
  • Problem is this layer is composed by countries, no smaller subdivisions... – Gerardo Jimenez Jun 21 '16 at 18:45
  • What centroid are you trying to get? One per country? – DPSSpatial Jun 21 '16 at 18:52
  • Yes, one per country – Gerardo Jimenez Jun 21 '16 at 18:52
  • Oh I see what you've done... just a moment... – DPSSpatial Jun 21 '16 at 18:57
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What you want to do is convert your polygons to centroids using the Vector > Geometry > Polygon Centroids tool in QGIS.

Then you'll end up with 1 point per country (but note the point will be weighted by all contributing features, ie. note how Alaska moves the 'centroid' of the USA to the NW part of the mainland)

enter image description here

You'll still have to attach values to the points in order to symbolize them as you're looking to do...

What the 'centroid fill' style is doing is placing a point for every part of the multi-part polygons you've downloaded...

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    Thanks your solution works, but also since the original file is composed by multipart polygons I also used vector/geometry/multipart to single parts. The only thing is select the exact polygon you want to use in the symbology. Imagine Korea, for instance, it has many islands. What I did is use the the select by area or single click tool to isolate the countries that I wanted to use. After that all worked fine. Thanks again Gerardo – Gerardo Jimenez Jun 22 '16 at 16:22

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