Module: src/pntToArea

Given a WGS 84 lon, lat pair, return the two letter code corresponding to the area that the point is in. The three polygons describe the regions covered by the 100 km squares for the British, Irish and Channel Island coordinate systems. These areas are exclusive. Where they overlap, e.g. British and Irish, they have been divided by a line through the Irish see roughly midway between the land masses. For the Channel Islands and Britain, the CI UTM 30 grid is truncated where it overlaps the British grid. The function returns the two-letter code corresponding to the area: gb, ir or ci. It returns null if the point doesn't fall within any of these areas.