Beyond just PostGIS, postgresql is a much better database on most fronts than 

If you have two tables, one with geometries and one with densities, they both 
need to have the same id somewhere. Once you have the join key, you can perform 
a join , not a union, to get a result set containing both the geometry and the 
density.  You can use raw SQL in qgis, but I tend to create a view in the 
database based on the query and the qgis will treat that as a table, more or 


On August 1, 2016 7:35:18 PM EDT, Chuck Young <> wrote:
>I have been using databases for years and have used QGIS since 1.8 for
>general mapping.  I know it can use additional data attached to the
>geographic data via a union query to display lots of different things. 
>have map areas where population density would be nice to display using
>different background fill colors bases on that density. I just need a
>of a boost getting the idea as to how to start and which way to go.
>I have been using the program with SpatiaLite database.  Do I need to
>tto the PostGis db?  Most of my other data is currently in MySQL.
>Thanks for amy advice / guidance!!
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