[Tagging] coastline v. water

[Ture Pålsson]

I mentioned the problem of mapping "fuzzy" areas to a friend, who 
replied along the lines of "why, of course such areas should be mapped 
as functions, taking a point as input and returning a real between 0 
(definitely outside) and 1 (definitely inside)!".

I'd rather not have to implement that, though. =)

(And I agree with Kevin about reconstructing an area from a point + 
surrounding coastline. I'd like to see at least an outline of an 
algorithm for that! Having said that, I also recognise that 
gazillion-point polygons to outline Skagerrak, Kattegatt, the North Sea 
and what-have-you may not be the prettiest state of things either...)