The Web Mercator Projection

An important consideration when preparing your data for display on web interfaces, is that most online GIS maps (often called “slippy maps” because of their instant loading with zooming and panning enabled) are projected into the Web Mercator Projection.

Mercator is a cylindrical projection.







Like all map projections, accuracy is greatest at the line of intersection, and increases in features toward the poles. For this reason, Mercator, being one of the most common projections used for global display maps, is cited in distorting people’s perception of the shape and size of Greenland. Seen below in this common Mercator display map, you can see how its easy to think Greenland is much bigger than it is.




Margaret Spyker

Trackbacks & Pings

  • Data Integrity | Web Map Academy :

    […] The earth is round and maps are flat – try to flatten out an orange peel and you’ll instantly see why distortion is introduced in this transformation from 3D to 2D – it is just inherent to working with geospatial data – the algorithms for these transformations are housed in Datums and Projections. Beyond this inherent transformation are also transformations between Datums and Projections that are often required by an analyst to use varying datasets with each other. That is to say, if you’re combining watershed data that is sponsored by the USGS and it is in a UTM coordinate space, and you want to combine it with state sponsored roads layers that use a localized projection system (like State Plane coordinates) – you’re going to have to warp one to the other. Depending on the output use of your data, you might have to warp them both to a new projection, as in the case of web mapping where most envirnoments use the Web Mercator Projection. […]

    3 years ago

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