Google Maps made the world a square of tiles, and Web Mercator became the map standard

In 2005 Google Maps faced a rendering problem: a seamless, fast, zoomable world map over ordinary web connections. Its solution combined two choices that are now taken for granted — use a Mercator-style projection with a spherical formula, and cut the map off near ±85° latitude so the projected world is exactly square.

With a square world, tiling becomes trivial arithmetic: at zoom 0 the whole map is one 256×256-pixel tile; every zoom doubles both axes, so each tile address is a pair of integers and each zoom level quadruples resolution. Tiles can be pre-rendered, cached and fetched independently — the property that made panning and zooming feel instant. Google's own documentation still describes the 256×256 base tile and the ±85° cutoff "to make the resulting map shape square, which allows easier logic for tile selection."

The scheme spread by compatibility. The EPSG registry records the projection as "WGS 84 / Pseudo-Mercator" (EPSG:3857), scope "web mapping and visualisation," used by Google Maps, OpenStreetMap, Bing, ArcGIS and ESRI; Esri even moved ArcGIS Online onto the same Mercator-based tiling scheme in 2009 rather than fight it.