Two problems with Google Maps for aviation

I love Google Maps and their API, and am using it extensively in my new web site OurAirports. However, there are two problems that keep coming up for using Google Maps with an aviation application:

[Diagram of Mercator projection]

  1. Google Maps uses a Mercator Projection, grossly distorting the northern and southern parts of the world, and cutting off the area near the poles so that a few of the Antarctic airports don’t show up on my maps at all. I can understand the reasons for their choice, with simple panning and tile paging and a rectangular area, but it can make things look pretty silly sometimes (such as Greenland and Africa appearing the same size).
  2. Google Maps does not provide an API call to draw a great-circle path. This seems to me to be almost a no-brainer, and it’s especially important in a Mercator projection, where the apparently straight paths drawn by the API are anything but (especially east-west). After messing with some out-of-date third-party libraries, I finally found some JavaScript at one site that does a good job on efficient, approximate great-circle paths, and am waiting to hear from the author about terms for reuse. Google might want to just go ahead and add this, though.

[Diagram of Mercator projection]

Aviation charts mostly use a Lambert conformal conic projection, which ensures that distances are preserved (any two points the same distance apart on the chart are the same distance apart in the real world); however, by definition this projection can’t show more than half the world at once, and generally shows much less than that, so it wouldn’t work for something like Google Maps.

About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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4 Responses to Two problems with Google Maps for aviation

  1. Sean Gillies says:

    In the digital age, distortion on the screen isn’t a big deal so long as your users have tools that measure actual distances and areas correctly, but if you really want conformal projections, there are good open source map and cartography engines. FlightAware uses MapServer: http://mapserver.gis.umn.edu. For the browser, you might want to check out the MapBuilder project. They were porting the PROJ.4 library to JavaScript and might be done by now.

  2. Ed Davies says:

    “…which ensures that distances are preserved (any two points the same distance apart on the chart are the same distance apart in the real world)”

    I don’t think any projection from a curved surface to a flat plane can preserve distances. As I understand it, the Lambert conic conformal is just a better approximation to this than most.

  3. Keith Golden says:

    Actually, there is an API to draw great circles. It was added in v2.84 of the Google Maps API:

    http://www.mibazaar.com/2007/07/geodesic-polylines-on-google-maps.html
    http://googlemapsapi.blogspot.com/2007/07/v284-changes-ggeoxml-methods.html

    Enjoy!

  4. david says:

    Thanks for spotting that, Keith — I’m glad that Google has added great circles after all. Right now, the segment resolution is a bit too coarse (the great circles look pretty chunky), but I’m sure Google will deal with that soon.

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