S pixel = S tile / 256 = C ∙ cos( latitude) / 2 ( zoomlevel + 8) For example on the equator and at zoom level 0, we get 40 075 016.686 / 256 ≈ 156 543.03 (in meters per pixel). Where C means the equatorial circumference of the Earth ( 40 075 016.686 m ≈ 2π ∙ 6 378 137.000 m for the reference geoid used by OpenStreetMap).Īs tiles are 256-pixels wide, the horizontal distance represented by one pixel is: S tile = C ∙ cos( latitude) / 2 zoomlevel The horizontal distance represented by each square tile, measured along the parallel at a given latitude, is given by: Such scale is typically used for the kind of area to represent on a single tile (Note that when rendering on the web, the standard CSS pixel size is defined at 96 PPI, browsers will rescale the images when needed but only by integer factors on PNG images to avoid making the rentered text or icons too fuzzy if the screen has a lower resolution, the rendered images may be larger and it's possible for a renderer to create image with other resolutions than 256 pixels at 96 PPI to better fit the expected sizes, and for a web interface to automatically select other available resolutions for Hi-DPI screens, but this requires more storage and computing resources on the server as well the zoom level in the formulas above do not necessarily need to be integers, and this may be used to get intermediate scales with tiles having more pixels). In addition, the given scales assume that 256-pixel wide tiles are rendered and will be dependent on the resolution of the viewing monitor: these values are for a monitor with a 0.3 mm / pixel (85.2 pixels per inch or PPI). "~ Scale" is only an approximate size comparison and refers to distances on the Equator.These values for "m / pixel" are calculated with an Earth radius of 6372.7982 km and hold at the Equator for other latitudes the values must be multiplied by the cosine (approximately assuming a perfect spheric shape of the geoid) of the latitude. Values listed in the column "m / pixels" gives the number of meters per pixel at that zoom level for 256-pixel wide tiles.The "° Tile width" column gives the map width in degrees of longitude, for a square tile drawn at that zoom level.This is useful when calculating storage requirements for pre-generated tiles. The "# Tiles" column indicates the number of tiles needed to show the entire world at the given zoom level.Variation with latitude of represented distances (in degrees or pixels) on the Mercator projection per actual distances (in meters) on Earth surface.
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