Unlike English "also", the particle も can be used when there is no explicit "similar" thing specified in the context. In such cases, も is closer to "even". Either way, the basic rule is も replaces を (and が, は).
笑っている人もいた。 There are even laughing people.
天才もミスをする。 Even a genius makes mistakes.
時が経つのを忘れた。 I forgot about the (passage of) time.
も is a very common particle. Some describe it as "inclusive", and it's often translated as "even / also / too".
In this particular context, the も implies that "even this suburb[an area]..." The underlying value judgment is that the subway is just so darn convenient, that it makes things so much better even in this area outside of the downtown.