Thursday, June 09, 2005

 

Why Google maps does not have a scale

One of the missing features from Google maps is a scale. Whilst not impossible to provide, there is one very good reason why this is not provided - Google maps are not drawn to scale!

This Slashdot comment titled Google Maps are awfully distorted anyway explains that

Google Maps uses a fixed longitude/latitude distance ratio of ~0.772, while the true ratio depends on latitude (the ratio should be cos(latitude)). So Google Map is optimized for 39.5 of latitude (N or S), and the maps are increasingly distorted as you go toward the poles or the equator.

The example given shows some streets in Anchorage which are really at right angles, but which show up as a diamond mesh due to the stretching. (Ignore the follow up comments that claim the original post is wrong - they are pointing out north south aligned grids, where of course the right angles are maintained by the stretching anyway). If you want a further example, switch to satellite mode, and observe the round structure to the north west of the runway - which due to the stretching appears as an ellipse shape.

Comments:
I have made some good enough measurement you can find from my blog. I help me as I always want to judge if the places are within walking distance.
 
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