What are map coordinate systems?

In this article, you will be guided through the core of every map in your MapTiler Cloud account – the coordinate system. You will learn why the coordinate systems are so important, what is a map projection or the specifics of the Web Mercator that is used by default in MapTiler base maps.

Important notice

There is no coordinate system or projection that would preserve areas, angles, distances and directions of the Earth precisely. You always have to think about the purpose of your maps, scale and type of data to choose the most fitting one.

Coordinate systems and why should you care

A coordinate system is the first important thing that you face when making a map from scratch. A map without it is subjected to oblivion in the geospatial world as it cannot be located. Coordinate systems are what make ordinary data geospatial. Thanks to them, we can navigate through maps reliably and with great accuracy.

Flattening the Earth

We of course cannot replicate the Earth’s surface as it is to our maps. To transform it from 3D to a 2D map layout, map projections are being used. These are mathematical algorithms within the coordinate systems. Coordinate systems define how to bind your map to the real locations on the Earth.

As the Earth is not flat, there will always be a distortion to some level when transforming it to the map. The important thing is what precision do we need the most. Map projections can either preserve areas, angles, distances, directions or compensate for all the distortions together.

Once we have the Earth's surface transformed to the map, coordinate systems ensure that we can navigate through it with a set of defined numbers – coordinates. When looking for a coordinate system, you may come across two terms – geographic or projected coordinate systems.

In the geographic coordinate system, the coordinates are related to an ellipsoid representing the Earth and are in the form of latitude and longitude. The most popular one is the World Geodetic System defined in 1984 (WGS84) which is used by GPS devices.

The projected coordinate system, on the other hand, is flat, represented by two axes with coordinates in meters or other linear units. Web Mercator is the most commonly used one. Adopted by Google Maps in 2005, it quickly became a de-facto standard for web mapping applications.

Web Mercator

Web Mercator, going also by Google Web Mercator, Spherical Mercator, WGS 84 Web Mercator, or Pseudo-Mercator, is the coordinate system which you will see most often on the MapTiler maps.

The original Mercator projection was mainly used for navigation purposes as it preserves angles and pictures loxodromes as straight lines. This helped the sailors to keep a steady course during their travels.

Web Mercator differs from the original Mercator projection in a far easier computation which is done on a sphere, instead of an ellipsoid. The entire world is shaped like a square making it easy to work with on the web. The north is always up on the maps and it reduces the area distortion on large scales, making it suited for seamless zooming with interactive world maps.

Despite its popularity in the online mapping world, Web Mercator has also its drawbacks. It distorts areas with distance from the equator, making Greenland almost the same size as Africa. Poles are not present on the Web Mercator maps and Antarctica is infinite in size. Therefore, it is not usable for polar areas at all.

EPSG.io

Need to quickly look up a coordinate system? Use EPSG.io – an open-source web service with a database of over 6,000 coordinate systems. You can search by name of the system, name of the covered country, EPSG or ESRI code, or any of the combinations of these.

Back when Web Mercator did not have an official EPSG code, EPSG:900913 was introduced by the open-source community. It is a reference to GOOGLE spelled with numbers. This EPSG became rather popular and is even included in the EPSG.io database. The official EPSG code for Web Mercator is 3857.

Coordinate systems in MapTiler Cloud

The dominant coordinate system for MapTiler Cloud base maps is the Web Mercator. However, you can also choose from other global or local coordinate systems based on your needs.

The Basic map style and OpenStreetMap tiles are both available in WGS84, ready to be adjusted to your brand. National maps come in their local projections as the national coordinate systems are carefully fitted for their corresponding territories. You can use base maps created specifically for France, UK, Switzerland, Netherlands, Czechia, or Japan which would be in line with your government’s requirements.

Lastly, it is possible to upload your own datasets in your favored coordinate system. MapTiler Engine will help you to process any of your geodata into tiles and upload them directly to your Cloud account.

Conclusion

A coordinate system is the core of every map. It allows us to transform any real location on the Earth into a flat map and navigate through it with coordinates. MapTiler Cloud base maps are by default in the Web Mercator (EPSG:3857) but WGS84 is available as well as local coordinate systems for national-specific maps.

Useful links

Local CRS in MapTiler Cloud
MapTiler Blog – OpenStreetMap in WGS84
MapTiler Blog – EPSG.io: Find Coordinate Systems Worldwide
MapTiler – Tiles à la Google Maps: Coordinates, Tile Bounds, and Projection
MapTiler Support – Engine: Coordinate systems
Esri – Coordinate Systems: What's the Difference?
QGIS documentation – Coordinate Reference Systems