OpenStreetMap – Do Tile Servers Typically Store Every Tile for Every Zoom Level?

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As I understand, a basic tile server provides raster image tiles for different zoom levels. To cover the world, it requires 1 tile at zoom level 0, 4 at zoom level 1, 4n for zoom level n. These are billions and billions of images that need to be stored in total for zoom levels 0 to 19.

My question is: Do tile servers typically in fact store all of these images? If not, how do they cover the whole world at every zoom level with tiles?

Best Answer

No, they don't store every tile. There are several reasons for this:

  • Size: Storing all tiles for all zoom levels would require more than 50 TB storage (source: Tile Disk Usage)
  • Gain: Typically, only 1.79% of all tiles are actually viewed since many just contain water or other uninteresting regions (source: Tile Disk Usage)
  • Computational costs: Pre-rendering all tiles would take a really long time.

Typically, tile servers pre-render some low-zoom tiles (let's say zoom levels 0-12) because they take long to render and will be viewed by many users. For higher zoom levels tiles are rendered on the fly and then cached for a certain time.

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