Rulebase symbology: Differentiated symbologies for same polygon layer presented based on hierachy (QGIS)

Question

TL;DR: Creating nice symbologies for a single layer, where a dotted line doesn't display underneath a dashed line, for sections where the dashed line is a symbology for a larger, more important area. In QGIS.

• How i would like the symbology to be:

• How the data is organized with filled polygons:

I'm new to the rule-based symbologies, and i have next to no SQL knowledges, so the solution doesn't strike me intuitively yet - although i see the great potential of the feature already, and thus believe that this is the way to handle it.

What i seek help to achieving, is portraying boundaries in a presentable way. Let's call them state and town administrative boundaries, as it is very much similar. I've created a polygon layer where i originally had the towns division, and arranged them into states and countries by attribute values. Now i seek to display it in a nice way. Lets say dotted line for towns, dashed for states and a full line for countries. Doing this by traditional simple symbologies creates a dotted line beneath the dashed, and i wish to avoid this. I'm convinced it can be done by rulebased de-selection of sections that is used for a higher level in the hierarchy, but can't figure it out.

Screenshot of the polygon layer i'm working on. Black borders are the smallest division, coloured areas are grouped by attribute field. And everything in this picture - besides the sea - is grouped by a second attribute as a third and highest tier, that i also wish to apply the symbology rule for in a full black border line, with the two divisions as dotted and dashed respectively, without interferearing each others.

Answer 1

Set the outline of the polygons to No Pen, then add an additional symbol layer of the type Outline: Simple line. There, you can make custom settings as shown in the following screenshot:

Edit

As you have everything on the same layer, you need to apply a different approach:

1. Create an own symbol layer for each admin level and order them accordingly (highest hierarchical level on the top).

2. To get the red outline, set the top symbol layer to type to Geometry Generator and paste this expression: buffer (collect( $geometry), 0), then style the solid outline. The expression creates one single polygon from all features.

3. To get the blue dashed line, this time in the Geoemetry generator paste this expression to get different polygons for each regional_admin level: buffer (collect( $geometry, group_by:="regional admin"), 0). Again style the line (I used Outline: Simple Line) to get the dashed blue line.

4. Repeat the same for the local level. Here, you don't need a Geoemtry generator, as each individual polygon should be represented.

5. If you now want to hide the black dotted line under the blue dashed line, there is a trick: click on the Simple Line entry (the one that generates the blue line, no. 1 in the screenshot) and press the green plus to add another line style. Set this (no. 2 on the screenshot) to a solid white line so that it covers everythin underneath: the black dotted line will be covered by the white one, whereas the blue dahsed line is still visible.

See details on the screenshot: