Zoom levels and scale
A zoom level or scale is a number that defines how large or small the contents of a map appear in a map view.
- Scale is a ratio between measurements on a map view and measurements in the real-world. When a map is displayed at a scale of 1:100 (or simply
100.0), 1cm on the display represents 1m (100cm) in the real world. A scale of
100,000.0means that 1cm on the map display represents 1km (100,000cm) in the real world, and so on.
- Zoom level is a number between 0 (global view) and 23 (very detailed view) and is used as a shorthand for predetermined scale values, but comes with some limitations.
Most web mapping APIs support zoom levels as a convenience. Zoom levels are only typically used for building applications that display data in Web Mercator projection. Scales are used to display data in any projection.
A brief history of zoom levels
Zoom levels were made popular by various web mapping solutions and APIs in the early 2000s. These adopted a tiling scheme that defined how a global map in Web Mercator projection could be pre-rendered for display in a web browser.
The tiling scheme is based on pre-rendering sets of 96 ppi 96 ppi (pixels per inch) is the standard CSS pixel size used by web browsers.
591657527.591555 is the map scale for zoom level 0.
96 ppi (pixels per inch) is the standard CSS pixel size used by web browsers.
Figure 1: A typical 256x256 pixel, 96 ppi, zoom level 0 image tile
Zooming in by one level halves the scale (and consequently quadruples the number of 256x256 pixel tiles required to cover the world - 2x the horizontal tiles, and 2x the vertical tiles). Zoom level 1 requires 4 tiles to cover the same geographic area as the single zoom level 0 tile; zoom level 2 requires 16 tiles; zoom level 3 requires 64, and so on. By the time you get to zoom level 20, 1,099,511,627,776 tiles are needed.
Crucially, these zoom levels represented scales at which the pre-rendered 96 ppi 256x256 pixel map tiles could be displayed crisply, without pixel resampling, in a web browser. Web browsers used the standard CSS pixel size of 96 ppi: that is, 1 tile pixel would match 1 screen (browser) pixel.
Over time, this mapping between zoom levels and map scales became established as a de facto standard, despite tiles being used outside of browser apps at many different screen resolutions, and despite the onset of dynamically rendered vector tiles in place of the original pre-rendered 96 ppi PNG or JPEG image tiles.
Many modern mapping solutions and APIs only display Web Mercator maps and so continue to use zoom level as a shortcut for map scale. They do this despite using vector tiles and vector data, which means they don't need to lock to these specific legacy zoom levels for a crisp map display that avoids pixel resampling, although many do.
Use this interactive tool to translate zoom levels to map scales:
This table covers each distinct zoom level and the map scale it translates to. Usage suggestions depend on the dimensions of the map view in question but are reasonable guides for a map in a typical web page.
|Zoom level||Scale||Usage suggestion|
|7||4622324.434309||Small country/US state|
|9||1155581.108577||Large metropolitan area|
To learn more, visit the Zoom levels OpenStreetMap page. .