The test, developed by Ghent University, presents you with outlines of two countries. Your task is to click the (+) and (-) until the bottom entity is the same proportional size to the upper one as they are in real life.
It's a bit challenging, in part because so many of our mental maps distort high-latitude regions. My results were so-so:
Apparently the set of maps offered varies, so you may get the same pairs I did. But feel free to post your results in the Comments. The test is here.
Via Neatorama.