When rendering the map the layers are drawn sequentially according to the layer order displayed by the layer panel. You might want to reorder the layer and set up a different order depending on the contents of the layers to make each layers visible by avoiding one layer hiding the features of another. You might also want to change the order of the classes and styles to provide the most appropriate look of the map by using the proper order.
The layers classes or styles can be reordered in the following 3 ways: