Creating thematic layers
In this example, called ch04_thematic, we will create an automatic solution for thematic mapping. It will include graduated and categorized symbology. To keep the example as simple as possible, we will make some generally incorrect assumptions. Firstly, we assume that we only have to style polygon layers. For graduated symbology, we hard code the intervals to five and also the color ramp starting from a beige tone and ending in a burgundy color. We will implement the whole code into our layer tree.
Extending the layer tree
We create the required GUI options in the layer tree. Firstly, we check against the origin of the layer. If it is a vector layer, we create an empty list and three buttons for the different styling options. Then, we save the default style in the layer, as it will enable us to restore the original styling. Finally, we register an event listener to the layer object. If the headers are changed, we rebuild the attribute list in the layer tree:
this.createRegistry...
