Making groups on cells when assign polygons

[thegreatkwanghyeon]

Hi, I'm trying to visualize an election map of South Korea.
There are provinces and cities and each province or city has number of electoral districts (represented as a cell).

I tried full map of South Korea and colored by province or city for convinience. As you see, some brown cells are apart from main body of the city. I hope cells belonging to the same city be adjacent to each other.

Can I make groups on cells in same city and make them be adjacent? Or any ideas that I can implement?