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For example, lets say I have two parallel roads with starting point and ending point 1 mile apart.

The left hand road is as flat and straight as an arrow.

The right hand road is also straight....but has a series of sine-wave shaped hills and valleys.

Obviously, if I measure using a Surveyor's wheel, the second path will be longer, even though both roads are starting and ending a mile apart.

My question: which measurement does google maps use? Does it account for difference in elevation adding to the travel distance?

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I doubt it. Since the length of a sloped road would be sqrt(1+x^2)-times the length of the flat one (where x is the slope). For low values of x, this is roughly 1+1/2*x^2, which is rather low, eg. for a 10 % slope, you get an error of 0.5 %. Not considering the actual lane you drive probably has a similar error.

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  • also in extreme cases a hilly road is likely to have speed restriction on it which routing algorithms can use to make a choice – jk. Oct 12 '11 at 13:54
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    Don't know why this was closed as off topic. I was planning on implementing a similar system for calculating travel distance in a game, and wanted to know how the big boys do it. Thanks for providing an example in the slope equation though. :). – waterwizard11 Oct 12 '11 at 15:01
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Even a very steep 10% grade is only 1/2% longer than a flat road covering the same horizontal distance.

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It does in cycling mode. Not because of the difference in the distance, but trying to minimise the total climb

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