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 100,000.0 means 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.

256x256 pixel PNG or JPEG image tiles, starting with a single tile at zoom level 0 that covers the entire world. This single tile, spanning -180º longitude to 180º longitude at 256 pixels width and 96 ppi, turns out to be of horizontal scale 1:591,657,527.591555 at the equator. So 591657527.591555 is the map scale for zoom level 0.

Zoom level 0 tile
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.

ArcGIS APIs can render many different map projections at a full range of scales, and so use scale rather than zoom level (although the ArcGIS JavaScript API does provide support for zoom levels as a convenience).

Conversion tool

Use this interactive tool to translate zoom levels to map scales:

NOTE: Mapbox zoom levels are one value less than ArcGIS API zoom levels.

Zoom level is predicated on a 256x256 pixel tile. Because Mapbox image tiles are 512x512 pixels, Mapbox zoom levels are 1 less than those of other APIs. For example: zoom level 12 in the Mapbox API is equivalent to zoom level 13 in other APIs such as the ArcGIS JavaScript API or Leaflet.

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 levelScaleUsage suggestion
0591657527.591555Global
1295828763.795777
2147914381.897889Subcontinent
373957190.948944
436978595.474472
518489297.737236Large country
69244648.868618
74622324.434309Small country/US state
82311162.217155
91155581.108577Large metropolitan area
10577790.554289
11288895.277144City
12144447.638572Town
1372223.819286Village
1436111.909643
1518055.954822Small road
169027.977411Street
174513.988705Street block
182256.994353Address
191128.497176Street intersection
20564.248588
21282.124294
22141.062147
2370.5310735

To learn more, visit the Zoom levels OpenStreetMap page. .

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