Heres an interesting one that I'm having a lot of difficulty with (i'm sure you maths boffins out there will scoff at my strugling with such a simple problem ) .

Given a set of lat\lon co-ordinates for a closed polygon shape how can I work out the surface area of that shape in sq miles or sq km (or feet or meters or something sensible!).

I've searched the internet but the solutions I find are all looking for the ultimate in accuracy and far to complex for me to understand! I'm really just looking at this from a 'Flat Earth' scenario it doesn't need to be extremly accurate (unless its just as easy to make it more accurate of course).