1. 空間の間隔だったら、「ま」でも「あいだ」でも可だと思います。They both tend to mean 間隔 but they have other meanings that differ but not in this context.
あいだ is the most closest to literally mean 間隔 or gap and works with both time and space. 間 works for space but means ひま、時間 when talking about time. 間もなく出発します。まだ間がある。間に合う。Kind of tricky to explain. Maybe somebody else can explain better.