How to create a graduated renderer for polygon borders instead of fills

Today’s post was motivated by a recent question on the #gistribe Twitter chat:

Is there a way in #qgis to have polygon outline colors changed the way the fill can be when you categorize data? #gistribe

—
Michele M Tobias (@MicheleTobias) March 11, 2016

So what’s the issue?

Default polygon symbols come with a fill and a border color:

When they are used in a graduated renderer, the fill color is altered for each class:

What if you want to change the border color instead?

The simplest solution is to add an outline symbol layer to your polygon symbol:

The outline layer has only one color property and it will be altered by the graduated renderer.

If you now hit ok, the graduated renderer will alter both the simple fill’s fill color and the outline’s color. To stop the fill color from changing, select the simple fill and lock it using the small lock icon below the list of symbol layers:

Voilà:

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.