Calculation of mileage on trails

[Namtrag]

Hi Everyone,

We have been throwing this around in my backpacking circle of friends for a while, and no one seems to be 100% sure one way or another.

I have the iPhone 6, which has a health app. One of the functions of the app measures how far you have walked that day. Invariably, when we hike in the mountains, the mileage the app calculates is appreciably higher than on the map or on the signs the trail has.

For example, we did a hike called Rock Castle Gorge from the hikingupward.com site, and it was listed at 10.7 miles. My wife's app measured over 14 at the end of the hike, and mine measured over 13.

One thing I reasoned is that the map mileage is calculated without taking into account the ups and downs of the trail...imagine a mountain shaped like a triangle, and you walk up one side and down the other. This would be the measurement the iPhone app makes, whereas on a map, the distance from the base on one side to the base on the other side is the distance calculated (like as the crows flies), which obviously is a shorter amount.

One reason I believe this may be the case, is we live where it is perfectly flat, and the app measures pretty close to the same mileage as the trail signs do at the local state park.

One guy I know is a surveyor and he agrees with my reasoning...that's how they do survey, as the crow flies. He said in the old days, they measured laying a length of chain on the ground, and repeating that process over the lay of the land. He said landowners get pissed when they have an old survey saying they have 600 acres, and he comes in a re-surveys it at 500 acres.

The implication is to me, we hike a lot farther in a day than we think!

Anyone have any thoughts on this? It's kind of mind blowing in a way...the AT could actually be a distance of 2800 miles if measured the way I am describing.