Monday, April 08, 2013

Mercator Projections & the Tissot Indicatrix


The introduction of draggable polygons into the Google Maps API has proved very popular with developers. A number of developers have used draggable polygons to demonstrate the effects of Google using the Mercator Projection in Google Maps.

Google itself created a demo game, called the Mercator Puzzle. The game uses a number of country shapefiles that when moved along the lines of longitude resize to show the country's correct size anywhere on the map.

Darren Wien's has also used draggable polygons to create a Draggable Tissot Indicatrix. This Google Map places a number of circles (all with a 500km radius) all across the globe. You can see how the Mercator Projection distorts the circles in the screenshot above. In the app itself all the circle polygons are draggable. So, with this interactive 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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