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I'm trying to make a species distribution project where I can select a species from a non-spatial list of species and the selection would highlight (select) all the counties to which the species has been attributed.

Simplified example data:
species, a non-spatial table of species (CSV with header):
"species"
"Mus borealis"
"Mus australis"

species_distributions, a non-spatial relation table (csv with header):
"species","county"
"Mus borealis","North"
"Mus borealis","Central"
"Mus australis","South"
"Mus australis","Central"

counties, a spatial feature class representing county boundaries (first row = field name):
"county"
"North"
"South"
"Central"
"West"

So if I select "Mus borealis" from the species table, the "North" and "Central" counties would be highlighted in the map. Seems like a simple scenario, but I have been unable to uncover a solution on my own. The closest I've found is a plugin "Select by relationship" but it doesn't appear to be available for QGIS 3 (I'm using QGIS 3.4.3). I have a PostGIS server available.

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First option is:

First open Plugins | Settings and enable Show also experimental plugins

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Now you can install Select by relationship plugin

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Now set up two relations in Project --> Properties --> Relations

First is:

  • Name: sc (or whatever)
  • Referenced Layer: species_distributions
  • Referenced Field: county
  • Referencing Layer: speciescounty
  • Referencing Field: county
  • Id: sc (or whatever)
  • Strength: Association

Second is:

  • Name: sd (or whatever)
  • Referenced Layer: species
  • Referenced Field: species
  • Referencing Layer: species_distributions
  • Referencing Field: species
  • Id: sd (or whatever)
  • Strength: Association

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Now activate the plugin and the relations.

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When you now open the attribute table of species layer and select your species, the countys will be highlighted.

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For my example I used exactly your species, counties and stuff. The one in the middle is "Central" and so on...

Second option is:

Use only species_distibutions table and county file. And select the species inside species_distributions. Add a rule based renderer to county file with the following rule is_selected( 'species_distributions', get_feature( 'species_distributions', 'county', "county")) and a second one with ELSE. When you now select the species/counties in species_distributions the counties will get a different style. This option was inspired by another great question/answer yesterday here: QGIS3: displaying (or filtering) features in one layer based on features selected in another. I bet there must be some way to also include species table and make your selection in there, but so far I could not make it work.. will update if I find a way.

  • First option works like a charm. You wouldn't believe how long I've been fiddling with this. I'll try the second option once I get over the euphoria. – Lee Jan 20 at 1:11

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