Darwin again

05-25-2007, 09:58

Here's something for the map/mileage/measurement experts. I know this is a little technical, but knowing the big brains (really:rolleyes:) that lurk here, there must be an answer just waiting to spew across our screens. So here's my thing:

We all know how vague the mileages are along the AT. The distance markers, the guidebooks, the maps, none of them really match. So, thinking about this, I measured the mileage along a section of AT in the Grayson Highlands two ways:

1) I used the linear scale along the bottom of the elevation profile; and

2) I measured the length of the line that traced the actual elevation profile, the one that goes up and down with the countours.

Result: Two different mileages. The first was seven miles, the second turned out to be 8.25 miles. Measuring the mileage on the map itself might yield yet another measurement. The section contained about 1,500 feet of climbing, then 1,000 feet of descent, then 1,000 feet of climbing.)

Given that it's shorter distance to walk in a straight, level tunnel through a mountain that it is to walk up and over that same mountain, it makes perfect sense that the more mountains you walk over, the more the actual mileage deviates from a one-dimensional measure taken from a map looking straight down on it. (Another example is the diameter of a ball versus the distance from one side to the other over the curved surface (half the circumference) -- the "over" distance is longer. Example: The distance from one side to the other, over the top of a 10-inch diameter ball is about 16 inches. You can see how walking over mountains could add mileage...)

I guess my question is, how do the major guides we use, (Wingfoot, ALDHA,) compensate for that up-and-down mileage gain? Or do they? It seems the only accurate way to measure the AT mileage would be with a wheel. I know I've heard that Warren Doyle and his crew walked a wheel up the trail once.

Given all the variables, there has to be a standard measurement. What is it and how close is it to the reality of the trail? Or have I made a fundamental thinking mistake here? Are the maps and guides made to comform to wheel surveys? If so, that would mean the mileages on the elevation profiles and maps are only useful as suggestions, more useful as agreed-upon conventions than actual figures. Has anyone ever done a three-dimensional AT mileage measurement (I mean, that we know of)? Even a GPS survey wouldn't take the extra up-down mileage into account.

We all know how vague the mileages are along the AT. The distance markers, the guidebooks, the maps, none of them really match. So, thinking about this, I measured the mileage along a section of AT in the Grayson Highlands two ways:

1) I used the linear scale along the bottom of the elevation profile; and

2) I measured the length of the line that traced the actual elevation profile, the one that goes up and down with the countours.

Result: Two different mileages. The first was seven miles, the second turned out to be 8.25 miles. Measuring the mileage on the map itself might yield yet another measurement. The section contained about 1,500 feet of climbing, then 1,000 feet of descent, then 1,000 feet of climbing.)

Given that it's shorter distance to walk in a straight, level tunnel through a mountain that it is to walk up and over that same mountain, it makes perfect sense that the more mountains you walk over, the more the actual mileage deviates from a one-dimensional measure taken from a map looking straight down on it. (Another example is the diameter of a ball versus the distance from one side to the other over the curved surface (half the circumference) -- the "over" distance is longer. Example: The distance from one side to the other, over the top of a 10-inch diameter ball is about 16 inches. You can see how walking over mountains could add mileage...)

I guess my question is, how do the major guides we use, (Wingfoot, ALDHA,) compensate for that up-and-down mileage gain? Or do they? It seems the only accurate way to measure the AT mileage would be with a wheel. I know I've heard that Warren Doyle and his crew walked a wheel up the trail once.

Given all the variables, there has to be a standard measurement. What is it and how close is it to the reality of the trail? Or have I made a fundamental thinking mistake here? Are the maps and guides made to comform to wheel surveys? If so, that would mean the mileages on the elevation profiles and maps are only useful as suggestions, more useful as agreed-upon conventions than actual figures. Has anyone ever done a three-dimensional AT mileage measurement (I mean, that we know of)? Even a GPS survey wouldn't take the extra up-down mileage into account.