Is your feature request related to a problem? Please describe.
At the moment, the show() method is used to plot values on top of a map using a colorbar e.g. confidence scores:

This method works well if your data is continuous. However, is confusing if you are plotting discrete data e.g. labels

Describe the solution you'd like
We should add an option to plot discrete values with a legend instead of colormap.
Ideally this could just be an arg like discrete=True to force the plots to use a legend vs colormap.

Describe alternatives you've considered
Make it clear in the docs that this is whats going on.