I'd be interested to see a map of the UK where each point was coloured according to where the water that falls on the land corresponding to that point reaches the ocean.
Here's an example of the kind of thing I'm thinking of, except that this isn't very detailed - while it looks right for the Thames basin, lots of smaller rivers get bunched together (for example in the South-West).
This is a bit more like it but for Africa. Note that there are some regions which do not appear to be adjacent to any coast - this means that all the water from these areas ends up in interior lakes and ultimately evaporates again. They are Endorheic basins.
