DataViz Tip #15: How To Choose A Map Projection
The earth is not flat, unlike what some people may think. The maps, on the other hand, are flat. In most cases what you are looking at is a view of the globe that someone created based on some algorithm. These algorithms are called projections and, as it’s impossible to convert a globe to a flat map without sacrificing any accuracy, they all have issues. So which one you use in your data visualizations is your choice and may differ based on what results you are after.
For good popular primer on projections, check out this video:
Or, if you are after a more encyclopedic information, check out the projections article on Wikipedia.
amChart JavaScript Maps support multiple projections which are set via the projection property. Let’s cover some of the available projections below and discuss scenarios when to use them.
Mercator
Mercator is probably the best-known projection. That’s what Google Maps uses and it’s a default in amCharts. The good thing about Mercator that shapes of objects are preserved. So it’s very good to use when focusing on small countries or just a small area on the map.
Where Mercator breaks down is in representing size. Objects are heavily distorted in terms of the area towards the poles. So northern/southern objects appear much bigger than they actually are. A fun way to explore this phenomenon is The True Size Of site where you can drag countries around the map and see how the size changes.
See the Pen dataviztip015-projections-mercator by amCharts (@amcharts) on CodePen.
Winkel Tripel
Winkel tripel is a compromise projection. It aims to minimize distortions in area, direction, and distance. This means that everything is distorted but in a balanced way making it a good choice for world-scale maps. Winkel tripel is used by National Geographic Society.
To use Winkel tripel projection with amCharts set projection: "winkel3".
See the Pen dataviztip015-projections-winkel3 by amCharts (@amcharts) on CodePen.
Eckert VI
Eckert VI is an equal-area projection meaning that areas of objects are preserved. Obviously, this is achieved by distorting their shape. So, this projection is a good choice when preserving the area of objects is very important yet shape is not.
To use Eckert VI projection with amCharts set projection: "eckert6".
See the Pen dataviztip015-projections-eckert6 by amCharts (@amcharts) on CodePen.
Miller
Miller projection resembles Mercator but improves it a bit in terms of object areas. It’s a compromise projection that gives you a familiar yet slightly more realistic look.
To use Miller projection with amCharts set projection: "miller".
See the Pen dataviztip015-projections-miller by amCharts (@amcharts) on CodePen.
Equirectangular
Equirectangular projection is a very simple projection where all the meridians and parallels are equally spaced straight lines. Since amCharts Maps do all the heavy lifting (in terms of projection calculations) for you there’s little reason to use this projection. However, if you want to do something special and overlay objects on the map outside the amCharts object, this projection gives you an easy way to do this since mapping of geographic coordinates to coordinates on screen is straightforward.
To use Equirectangular projection with amCharts set projection: "equirectangular".
See the Pen dataviztip015-projections-equirectangular by amCharts (@amcharts) on CodePen.
For list of other supported projections check out amCharts JavaScript Maps reference.
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