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Do You Really Know Where You Are?

2012 August 17

By Casey J. McLaughlin

Wikipedia: Mercator

Map projections have caused me great pain.  The standard Mercator map I grew up with became standard 500 years – shapes are well represented and any line drawn on the map represents a true compass bearing.  In other words, a Mercator map was incredibly useful for navigating and became the projection of choice for sea travel.  Take a step back and understand that a  projection is “a method by which the curved surface of the earth is portrayed on a flat surface” (ESRI GIS Dictionary).  Wikipedia has a good description of map projections. Seemingly a simple concept, there are several hundred types of projections.  Each has its own uses, but all flat maps contain distortion of some kind.

Greenland and Antarctica appear as huge white areas.  Notice the grid cells at the top and bottom are quite long.  This projection distorts area as you travel away from the equator.  Would you it surprise you that in reality, Africa is 14 times larger than Greenland?!   On the television series, “The West Wing” (Season 2, episode 16) character Josh Lyman asks a group of cartographers:

“Relative size is one thing, but you’re telling me Germany isn’t where we think it is?”

Dr. Fallow responds:   “Nothing is where you think it is.

Maps Without Bordes: Gall-Peters Projection

Casey McLaughlin is a first generation Geospatial Enthusiast who has worked with EPA since 2003 as a contractor and now is the Regional GIS Lead. He currently holds the rank of #1 GISer in the EPA Region 7′s Environmental Services Division.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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4 Responses leave one →
  1. Tomo Krajina permalink
    August 20, 2012

    I think another reason why Mercator hasn’t changed that much with the digital era is the web. Specifically google maps — it is easier (for google) to store and compute the map with images as rectangle files. With better browser support for vector imaging and better Javascript image manipulation capabilities — this should change. I hope :)

    • cmclau02 permalink*
      August 20, 2012

      It is interesting that we all follow behind the platform providers instead of demanding we use the best projection — of course the “best” projection really depends on your project needs. I think you’re right about why the popular vendors are using the Web Mercator projection — speed….which is why most developers make their web maps in Web Mercator since it makes our maps faster. If users must wait for something to load they’ll probably move onto something else. There is a great clip from West Wing about the social implications of using the Mercator map — its hilarious. The point is really that just because map making is easier (and GIS in general) doesn’t excuse users from knowing about the projection they’re using and what some pitfalls might be.

      • Tomo Krajina permalink
        August 21, 2012

        I must confess that I’m guilty, too :) I’m not a GIS specialist but a web developer with few sites (for example TrackProfiler) using some mapping features. I do remember about Mercator from elementary school. But Google maps was too easy to set up and I didn’t investigate the alternatives at the moment. I would like to have something else other than Mercator, but for the problem is that web tools at the moment aren’t ready :( I can create non Mercator maps as a static images, but I’d like my users to have zoom, drag-and-drop, editable maps, etc.

        Maybe with more modern browsers (still to come) one day…

        • cmclau02 permalink*
          August 21, 2012

          It is a process and an interesting one since most government data that I’ve seen is not natively created in the Web Mercator projection. At some point, processing speed may be sufficient enough so that the consuming software projects “on the fly” (ESRI’s ArcGIS does this) and the end user doesn’t notice anything. With the emphasis on mobile technology right now, speed is a critical design element. Projection comes into play quite often when reviewing different aerial photography since major vendors do it slightly differently and there isn’t always perfect agreement between them. I don’t get to do much of it, but there is certainly still reason for ground truthing!

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