The difference between XYZ and TMS tiles and how to convert between them
Lots of tile-based maps use either the XYZ or TMS scheme. These are the maps that have tiles
ending in /0/0/0.png or something. Sometimes if it's a script, it'll look like
&z=0&y=0&x=0 instead. Anyway, these are usually maps in Spherical Mercator.
Good examples are OpenStreetMap, Google Maps, MapBox, MapQuest, etc. Lots of maps.
Most of those are in XYZ. The best documentation for that is slippy map tilenames on the OSM Wiki, and Klokan's Tiles a la Google.