The tile pyramid
A web map is served as a pyramid of tiles. Each zoom level doubles the resolution, and the world at that level is cut into a grid of fixed size square tiles addressed by zoom, x, and y. Panning and zooming just request the tiles that fall in the viewport.
Why tiles work so well
- Cacheable. A tile at a given coordinate is the same for everyone, so it caches beautifully at the edge.
- Bounded work. A viewport needs only a handful of tiles regardless of how large the whole map is.
- Precomputable. Stable base map tiles can be rendered ahead of time and stored as plain files.
Static versus dynamic tiles
- Raster tiles are prerendered images, simple and cache friendly.
- Vector tiles ship geometry that the client styles and labels, allowing smooth zoom and per user styling at the cost of client work.
- Frequently changing overlays like traffic are rendered on demand with short cache lifetimes.
Key idea
Map tiles turn an unbounded map into bounded cacheable squares addressed by zoom and grid position so any viewport costs only a few requests.