Using Data Defined Overrides are a powerful tool in QGIS, but I’ve got the impression that too little people use this feature. So in this blog post you can learn what they are and I’ll show you a simple example of how to use them. You will notice this blog post is pretty long, but that doesn’t mean Data Defined Overrides are difficult, they just have loads of options and I wanted to show you every step I took to use them.
What are Data Defined Overrides?
In QGIS you can use data from a layer or an expression to change the value of a setting in a layer for that specific map object. This means that a setting is dynamically changed based on a value in the attribute table of that object or a value that is generated using an expression. In other words, if you use a Data Defined Override, the manually entered setting is ignored, and instead something else is used.