Monday, October 09, 2017

Working With Map Projections

Projection Face is a great illustration of the distortions created by different map projections. The interactive shows how 64 different map projections effect our view of the world by showing each projection's effect when applied to something very familiar, the human face.

The distortions of each of the different projections cab be illustrated further by clicking and dragging any of the mapped faces. This illustrates how the different map projections can be distorted themselves simply by changing the center of the map.

Projections Face is an interactive version of a 1924 illustration from Elements of Map Projection with Applications to Map and Chart Construction.

Degenerate State's Map Projections tool is another interesting visualization of how different map projections distort our picture of the world. Map Projections is a very similar tool to Projection Face but this interactive shows you how map projections actually effect maps.

The tool allows you to view a map of the world using 11 different map projections. This in itself is a good demonstration of the choices cartographers make when depicting a three dimensional sphere on a two dimensional plane. However Map Projections also allows you to explore how these different map projections would change if you changed the 0,0 point of latitude and longitude on the map.

If you click anywhere in the world then the map will automatically change to show the distortion needed if this was the origin of the map.

If you want a little help deciding which map projection you should use for your current map project then you can use the Projection Wizard to decide on the best projection.

This map projection guide allows you to select the extent of the map view you are working with by outlining the area on a Leaflet map. Once you've highlighted your map bounds you can choose a distortion property (Equal-area, Conformal, Equidistant or Compromise).

The Projection Wizard will then suggest which map projection you should use depending on the extent and the distortion property of the map. The suggested projections are based on 'A Guide to Selecting Map Projections' by the Cartography and Geovisualization Group at Oregon State University.

A Proj.4 link is provided next to each suggested projection, which opens a popup window with a Proj.4 library. Once you've settled on your map projection you might want to check-out the Proj4Leaflet plugin for using projections supported by Proj4js with Leaflet powered maps.
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