Hi, there are assorted free aviation maps floating around the internet such as 'Plan-G', here's a small section of one showing airfields in Norfolk (England) but i can't find a key to indicate what kind they are, does anybody know?
As you see, there are 4 types, red/black/filled runway/unfilled runway, but why 4 types, are some military or non-military, hard runway or grass field etc?