Map ground resolution and scale

Model: cos(lat) × 2π × 6,378,137 m / (tile size × 2^zoom); scale = resolution × 96 / 0.0254

Accuracy: Exact on the Web Mercator sphere

When to use this: Use this when choosing a zoom level: the meters each pixel covers and the map scale at a latitude, for 256 or 512 pixel tiles. It is what connects a required ground resolution, a print scale, or a source imagery resolution to the zoom a map should serve. It is also how to check whether a tileset can support a measurement: if a pixel covers two meters, nothing read from it is good to half a meter.

Limitations: Resolution in Web Mercator changes with the cosine of the latitude, so a zoom that gives half a meter per pixel at the equator gives much less at sixty degrees. Scale also depends on the display's pixel density, and the number here describes the projection rather than the detail actually present in any particular tileset. The map scale it reports assumes a nominal screen pixel size, so a print or a high-density display works out differently.

Worked example: 40.446° at zoom 12, 256 px. Source: add-spatial-indexing-and-raster scenario: about 29.08 m/px.

Review: Not yet independently reviewed by a GIS professional.

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-19, changed: Every indexing tool is now stable. Geohash decode and neighbors match pygeohash on 1,000 and 500 cases; the Plus Code tools pass every row of the Open Location Code test data; tile ground resolution matches the Bing Maps table; the H3 resolution chooser matches H3's resolution table; and H3 polygon fill gives H3 C's own test counts (1,253 cells, 1,214 with a hole). Results are unchanged apart from the fix below. Changelog

Checked against: 30 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• Bing Maps Tile System, Microsoft, Online documentation. Tile coordinates and quadkeys; ground resolution = cos(lat) × 2π × 6,378,137 / (256 × 2^level).
• Slippy map tilenames, OpenStreetMap Wiki, Current wiki page. Lon./lat. to tile numbers, tile numbers to lon./lat., resolution and scale.