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I am working in QGIS 3.8.3-Zanzibar on a shapefile with polygons.

I am zoning by selecting the polygons and giving each group a different number (a zone code).

In order to visualize it, I have a Category Thematic map with the zone number, so I can easily see the different groups I am creating.

zoning progress

But, as I keep on making groups (that is, giving other zone codes to the polygons), it is hard to visualize the result unless I manually update the thematic map.

I would like the map to dynamically change its colours as I change the zone numbers. Until now, I have to re-classify the categories of the thematic map, as it only classifies with the existing numbers (zone codes) but the new ones I give out, the all go to the group of "all other..."

categories and "all other..."

Here I am going to show my work routine with sample data, as suggested:

  1. Initial shapefile with polygons. Visualization is simple symbol.

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  1. Visualization with a Category thematic map depending on the zone number (last column of my table).

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  1. I select some polygons and change their zone number.

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  1. The visualization has change according to the new zone number of the polygons.

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  1. I then change other polygons zone number.

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  1. The visualization changes again, but with the same colour, because any other zone numbers are classified as “all other”.

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  1. I would like to have this visualization without having to manually update the categories of the thematic map.

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I don't know how to upload shapefiles, in order to provide the sample data, but here it is a screenshot of my table (it really only matters the last column).

Table

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  • I tried to explain the routine better, but I don't know how to provide shapefiles. I hope the new images help. Thanks a lot.
    – Pescariz
    Commented Jan 3, 2022 at 10:12
  • What is range of the zone numbers?
    – Kadir Şahbaz
    Commented Jan 3, 2022 at 16:29

2 Answers 2

Reset to default
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A workaround would be like this:

  • In Style Panel, type $id for "Value".
  • Click on "Classify" button. This generates separate symbols for each id.
  • Change $id to ZoneID.
  • Now, there is a color for each zone id. I assume that the range of ZoneIDs is the same of the feature ids. You may need to refresh map canvas (F5) to see the result.

enter image description here

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To avoid manually updating the categories, simply click the Classify button each time you made a change:

enter image description here

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  • If I do that, I get the same colour as before, plus I was trying to avoid the manually click (I have many zones to change). I was hoping there was some sort of dynamic update of the thematic map.
    – Pescariz
    Commented Jan 3, 2022 at 10:30
  • This should be possible using PyQgis - however, due to the policy of this site, questions asking for Python should include some code attempts.
    – Babel
    Commented Jan 3, 2022 at 10:33

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