The numerous parallel dotted lines on this map indicate the location of an important feature on the landscape. What is it

East African Rift

Explanation:

East African Rift is a continental rift zone in East Africa that is approximately 7,000 kilometres in total length. It runs from Lebanon  to Southeast Africa.

The numerous parallel dotted lines on the map indicate the location of an important feature on the landscape. It is East African Rift.

So, answer is East African Rift.