Improve select area visuals

Improve the aesthetics of plotting select_area. Eg remove boundaries of neighbouring regions (if desired)

Below, is an example of the current output. It is preferable to only plot the borders of the region you are interested in, or have the choice whether or not these other borders are shown.

A possible solution may be to select only the `select_area` in the `regions` object within the function (and drop the other areas).


Start by locating the plotting function that implements select_area and inspect how the regions object is used. Reproduce the example output, then verify that neighbouring-region borders can be omitted or controlled while the selected region remains plotted.

Written by the indexing model from the issue text.