First choose any South American 50K+ city by entering it and choosing it in the drop-down box. Then, name the 3 largest South America cities in each 100 km circle/ring as the rings expand outward from your city of choice. The first circle will include your city of choice as a possible answer if it is among the 3 largest in that area. As you enter cities you will see their rank within the current ring (1st, 2nd or 3rd largest) above their marker.

When you run out of time or end the quiz, you will see the current ring’s correct answer at right (under ‘Answer Stats’ by your coordinates).

For example, if you choose ‘Buenos Aires’ – you will be shown a circle of radius 100 km centered at Buenos Aires. Naming all of the 3 largest 50K+ cities in this circle (Buenos Aires in this case is one) will cause another ‘ring’ of radius 100 km to appear outside that circle. You now need to name the 3 largest South America cities in that ring (but not within any previous circles/rings). If a city is not within the next ring of that distance, the ring will keep expanding by that distance until at least 1 city falls within it. So if a city doesn’t fall within 100-200 km, it will expand to be a 100-300 km ring, then 100-400 km and so on until a qualifying city is found within the ring.