Probably more amusing than useful, this table by Sophos is a table of where spam is inserted into the Internet mail system. This is not quite the same as where the spam comes from, because most spam is distributed via an infected host of some kind; such as your desktop PC (if it gets infected).
It is essentially a list of where the most infected PCs can be found. If you click through to the Sophos article itself, you get a longer explanation of what is going on here.