How do I Go about making a interactive Border?

Let me explain. Here's a World Map with no Borders

gyazo.com/fe7d04d75b1bfa2f7bc0a071a34b35e3

Let's say i place an object. A Command Center, within this command center's borders, you can build any smaller objects, houses, businesses, etc. In Order to expand your border, you must place down another command center. If (Command center Borders) are near each other. instead of overlapping like this gyazo.com/32a77ea5e1af82823f0751262fc852aa

I would like the borders to connect similar to

gyazo.com/8ce720d1913fd553420b5fcd8849fd52

How would I go about making this?