How a map works, Mercator, tiles, and your GPS pin (opens in new tab)

You drag a map, it loads more map. You drop a pin, it lands exactly where you tapped. This feels like one seamless thing, but underneath, every "slippy map", Google Maps, OpenStreetMap, the map in a thousand apps, is built from two pieces of math: a way to flatten a round Earth onto a flat screen, and a way to chop that flat image into loadable squares. Both fit in a few lines of Python. Learn them and your blue dot stops being magic: you will be able to take a latitude and longitude and comp...