consider the following two populations:
which one has the most diversity?
one might be tempted to think that A (a scenario that might occur if two populations are forbidden from interacting with each other) has more diversity: it has 2 colors (red and blue) instead of 1 (purple).
however, when you look more closery, B has actually a lot more colors: in-between the mass of purple, there are reds, blues, and many in-betweens. at the fine grain level, there's a lot more diversity, even if the whole looks more homogenous from above.
which one is true diversity?
my argument would be that it is B; you should care about the actual state of the territory in the day-to-day interactions of elements of these populations, not the overall appearance of the map, as they may appear to a state for example.