Wednesday, October 11, 2017

Demonstrating the Mercator Problem


On Monday, in Working with Map Projections, we explored how different map projections distort our picture of the world. The Mercator projection is undoubtedly the most common mpa projection used in modern online interactive maps. It is therefore worth taking a closer look at the particular distortions of Gerardus Mercator's popular map projection.


The Mercator Problem is an informative introduction into how the Mercator Projection distorts the map of the world. The problems with the Mercator Projection are well known. The projection distorts the scale of areas along the lines of longitude. Therefore areas close to the poles seem far bigger than areas close to the equator. Which is why Greenland on maps often seems to be about the same size as Africa (it isn't).

The Mercator Problem includes a neat demonstration of the way that the Mercator Projection distorts the size of countries depending on how close they are to either pole. An interactive comparison tool allows you to view how two countries appear on a map using the Mercator projection and how they should appear if the land area of the two countries were more accurately portrayed.



Darren Wien has also created a neat demonstration of how the Mercator Projection used in Google Maps distorts objects close to the poles. His Draggable Tissot Indicatrix uses draggable polygons to demonstrate how areas are distorted as you move nearer or further from the poles on Google Maps. 

His Google Map includes a number of circles (all with a 500km radius) placed all across the map. You can see how the Mercator Projection distorts the circles in the screenshot above. In the app itself all the circle polygons are interactive. So, with this Tissot Indicatrix, you can actually move the circles around the map and observe how they grow and shrink along lines of longitude.
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