This function is to be used to get width and height values
for maps created in reports (*.Rmd, *.qmd).
It uses the width / height ratio of a spatial object bounding box to find a
matching ratio for the map.
If width is specified, then height is deduced from the width / height ratio
of x, figure margins and title size.
If height is specified, then width is
deduced from the width / height ratio of x, figure margins and title size.