patient origin area for each health center is blue color and unique.
when you select 2 health center, which next to each other, there are very likely their patient origin area are overlapped.
you can use light to dark blue color to tell which area are overlapped.
no overlap is light blue,
2 overlap is darker blue.
3 overlap is more darker blue.
4 overlap is more and more darker blue.
and so on
Original UDS use 1 to 6 pattern to show how many overlapped.