The halacha of techum states that one cannot go more than 2000 amot outside of his place of rest. The place of rest can be the city in which he's spending Shabbat.
With regards to t'chum, what constitutes a city?
If there are two municipalities touching, is that one or two? On the flip side, if there is one municipality with lots of empty space, is that one or two?
Does it reach until municipal limits?