[Qgis-community-team] Choropleth mapping

[David Rhoads]

Folks:

Please help me.  I am very frustrated.  I recently downloaded the 
current long-term release of QGIS (3.16.8).  Two of you kindly suggested 
documentation to get me started.  One problem, the documentation does 
not match the current shipping version of QGIS. In one case, the 
documentation was for QGIS 1.  In the other case, while supposedly for 
QGIS 3.16, the screens in the documentation do NOT match what I see in 
my version of QGIS (I'm running Win 10).

I am starting with a series of districts in a county.  I want to do 
choropleth mapping in those districts based on numeric values in a CSV 
file.  I am able to load the two layers, the districts from an SHP file 
and the numeric values from the CSV file and then to join them.  When I 
try to generate the choropleth map, the name of the field containing the 
numeric values does not show up when I click on the Symbology tab.  I 
can see that field in several other tabs, but not in the Symbology tab.

I expect there is an easy solution to this, but so far it has eluded me.

Attached are the Project file and the CSV file containing the data 
(Value-1) to apply to the polygons.  Join is done on the PrecinctID column.

David

On 7/1/2021 1:20 AM, Evan Derickson wrote:
> Hi David,
>
> You can use the Graduated symbol renderer to make a choropleth map. 
> The official documentation on this is at 
> https://docs.qgis.org/3.16/en/docs/gentle_gis_introduction/vector_attribute_data.html#graduated-symbols 
> <https://docs.qgis.org/3.16/en/docs/gentle_gis_introduction/vector_attribute_data.html#graduated-symbols>, 
> but you may find something like 
> https://guides.library.duke.edu/QGIS/Symbolize 
> <https://guides.library.duke.edu/QGIS/Symbolize> to be more helpful.
>
> Best,
> Evan
>
> On Wed, Jun 30, 2021, 14:46 David Rhoads <dgrhoads at dgrhoads.us 
> <mailto:dgrhoads at dgrhoads.us>> wrote:
>
>     Does QGIS support choropleth mapping (i.e. ability to apply colors to
>     polygons depending on a numerical value associated with each
>     polygon)?
>     Our application has to do with looking at the relative statistics of
>     voting precincts in Chester County, PA.  We want to easily find
>     outliers.
>
>     If so, where in the documentation is this described?  I've done some
>     looking and have not been able to find anything related.
>
>     Thanks,
>     David Rhoads
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