Plot one colour per region

Currently, we plot data per grid and we can overlay region boundaries.
Future development should consider providing one colour per region. See below for an example from ABS with their data

The following links may be helpful:
* https://stackoverflow.com/questions/49564810/coloring-a-maps-region-based-on-poll-data-using-python
* https://python-graph-gallery.com/choropleth-map/
* https://stackoverflow.com/questions/56690524/matplotlib-geopandas-plot-chloropleth-with-set-bins-for-colorscheme/56695238#56695238