What’s a map projection?

At the most basic level, map projections are how we turn the 3D earth surface into something flat. There are polar projections that look at the globe from the top or bottom view, or more common projections that are centered near the equator. Map projections are really easy to overlook, but have large impacts on how we perceive space.

When you turn the surface of a sphere into a flat object, you will get distortion of shape, size, or distance of map formations– you cannot maintain fidelity of all three. The projection you choose should be reflective of the end use of your map. If you’re looking to plan a route between two points, use a projection that maintains accuracy of distance. The stereotypical map you learned in school and may have hanging in your home uses the Mercator projection, which stretches land masses near the poles and compresses land masses near the equator. This makes Europe and North America look a lot bigger than South America and Africa.

cnn_mercatorslider.PNGIn 2017 CNN had an excellent article with fun sliders showing the size distortion of the Mercator projection (see image above, and follow the link to play with the sliders). It goes into some of the history of the projection, explaining why they chose to make meridians and parallels truly perpendicular to each other despite the related distortion.

It’s easy to minimize problems when they look small on a map– we consciously or unconsciously prioritize the needs of countries that are perceived as larger, and the social consequences can be huge. Every now and then people remember that the Mercator projection is misleading, and there are alternatives. Check out this clip from the West Wing that aired in 2001 comparing the Mercator projection to the Gall-Peters projection.


The big take away is that maps can be misleading and projections matter. The next time you see a globe, look at the shape, size, and relative position of land masses– it probably differs from what you expect. Next week I’ll talk about two datums, NAD83 and WGS84, that are commonly used for GIS applications and the projections related to them.

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