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I am a total beginner to QGIS and still struggling with the basics. After a quick research on this forum I could not find the answer to my current issue.

What I am trying to do is to colour the regions of a country shapefile where using the information stored in a series of categorical variables. So for each variable if that category is "yes" I want the region to be coloured in one colour (also I would later like to have a legend for the colours, but I'll worry about that later..). I have started doing this using rules-based styling in the attribute table, but I am unsure how to do it when there is conflicting rules, when a region has multiple entries of "yes". If I use single rules, then colours are overwritten by the rule hierarchy. Ideally I would like to have this region colours in stripes.

Does anybody have an idea how to do this?

Here is a description of my data structure.

enter image description here

Community
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Papayapap
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  • Take care of https://gis.stackexchange.com/questions/3087/what-makes-a-map-be-classed-as-badly-designed – AndreJ Nov 19 '18 at 11:07

3 Answers3

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If you have only a few categories, you can create a separate rule for each possible combination of yes's and no's, for example if you have only two categories, your set of rules would look like this:

"cat1" = 'yes' AND "cat2" = 'yes'
"cat1" = 'yes' AND "cat2" = 'no'
"cat1" = 'no' AND "cat2" = 'yes'
"cat1" = 'no' AND "cat2" = 'no'

The number of possible combinations is the square of the number of categories (3 categories = 9 combos; 4 categories = 16 combos; 5 categories = 25 combos; etc.). This quickly becomes an unmanageable number of combinations. So a more automated solution would be best with more than 4 categories.

Let's set this up with nested rules. The larger rules will group categories by how many different 'yes' categories they have. A true/false statement like ("cat1" = 'yes') will evaluate to 1 when true, 0 when false. So a sum like this:

("cat1" = 'yes') + ("cat2" = 'yes') + ("cat3" = 'yes') + ("cat4" = 'yes')

will give a count of how many of the categories say 'yes'. Create 5 rules without symbols, like so:

("cat1" = 'yes') + ("cat2" = 'yes') + ("cat3" = 'yes') + ("cat4" = 'yes') = 1
("cat1" = 'yes') + ("cat2" = 'yes') + ("cat3" = 'yes') + ("cat4" = 'yes') = 2
("cat1" = 'yes') + ("cat2" = 'yes') + ("cat3" = 'yes') + ("cat4" = 'yes') = 3
("cat1" = 'yes') + ("cat2" = 'yes') + ("cat3" = 'yes') + ("cat4" = 'yes') = 4
ELSE

Nest 4 rules under the first rule, with simple fill style: "cat1" = 'yes' "cat2" = 'yes' "cat3" = 'yes' "cat4" = 'yes'

Choose the colors you want. Save the colors as swatches to make them easy to access in the following steps.

Right-click on the second rule > Refine Current Rule > Add Categories to rule. Create a style with two stripes.

  • Line pattern fill, set line width to 1/2 the value you choose for line spacing.
  • Add a second layer to the simple line (under line pattern fill). Use the same line width as the first layer; use the same number for "offset".

enter image description here

Add 5 styles, then return to the main style panel screen. Change the rules as follows:

("cat1" = 'yes') and ("cat2" = 'yes')
("cat1" = 'yes') and ("cat3" = 'yes')
("cat1" = 'yes') and ("cat4" = 'yes')
("cat2" = 'yes') and ("cat3" = 'yes')
("cat3" = 'yes') and ("cat4" = 'yes')

Change the stripe colors to match the colors you used for the single-category group. Use color swatches to get exactly the same color.

Repeat for the 3-category and 4-category groups.

csk
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  • Thanks csk, this sounds like what i wanted to do. I will try to implement it. – Papayapap Nov 22 '18 at 05:22
  • Actually, I think I will need to do the unautomated solution, because, if I get it correct, because I don't only need the count of yes. – Papayapap Nov 26 '18 at 07:32
  • Somehow, when I do this approach with many lines, they always overlap. Did you also get this problem? – Papayapap Nov 29 '18 at 09:23
  • I didn't try it with more than two lines, but that doesn't surprise me. I've had a similar issue with other symbol types, where the offset doesn't give a consistent appearance. – csk Nov 29 '18 at 17:37
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If you have in the attribute table YES and other strings as shown in the image below, you can do the following:

enter image description here

  • Go to Rule-based Style
  • Add this Rule in the Filter: "FieldName" = 'YES' #You need to change FieldName based on what you have in the attribute table. In this Example: "YES_NO" = 'YES'

enter image description here

  • Add a new rule and in the Filter section select ELSE

enter image description here

  • The Rule based Style should look like this:

enter image description here

Here is the output:

enter image description here

ahmadhanb
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  • Thanks ahmadhanb for the very clear illustration. However, for me I know how to do the single rule colouring. What I am struggling with is how to do it with multiple rules. In my data I have 6 yes_no variables and I need to colour the map with different colours for each indicator. So, I will have overlaps where more than one variable has the answer "yes" and then there will be conflicting colours. Do you know how I can do it such that in this case the field will be striped with both colours? – Papayapap Nov 19 '18 at 13:12
  • @Felix Could you please add a screenshot of part of your attribute table so that your idea can be clear to the community? – ahmadhanb Nov 19 '18 at 13:37
  • You need to look at the conditional expression. A case statement should be able to do what you are looking for – kartoza-geek Nov 19 '18 at 16:38
  • Dear ahmadhanb, I have added a fictional screenshot of my data in my question. Thanks @kartoza-geek for the hint on conditional expressions. Could you perhaps expand on it? – Papayapap Nov 22 '18 at 05:19
  • @Felix You are making things complicated, you can simplify use categorize symbology and classify by region field. Then use a table whether in the layout or the manuscript to define what each region represents. – ahmadhanb Nov 22 '18 at 07:59
  • Dear ahmadhand, thanks again for the tip! Unfortunately I was not able to find the "categorize symbology". Could you also explain how to do this? – Papayapap Nov 26 '18 at 07:30
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You can use a nested rule based symbology like this:

enter image description here

The hierarchy order starts at the bottom. Means: if one polygon has 1 = yes and 2 = yes it will use the style of 2. Using transparent styles (like 3 and 5 within 1; the polygon in the middle in my example) you can also use combinations.

MrXsquared
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