Route 459287 - Appalachian Trail from Lehigh Gap - Elevation

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Flagday53
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Joined: Tue Jul 24, 2012 3:31 pm

Route 459287 - Appalachian Trail from Lehigh Gap - Elevation

Post by Flagday53 »

I volunteer at a local nature facility at the Lehigh Gap. People come in for info and ask about the trails at our location and the Appalachian Trail which is nearby. I traced the AT from the Route 873 parking lot to nearly just over the Lehigh Tunnel of the Pennsylvania Turnpike, just to give people an idea of what a five-mile hike would involve, mostly in terms of elevation changes.

According to the elevation map on the above route, the change is "1900 feet" up and down. From my calculation, the highest point on this route is 1581 and the lowest point is about 440 for a straight-line climb of 1141 feet. The difference between 1900 feet and 1141 feet is 759 feet.

Question: do all the ups and downs on this hike actually add 67% MORE elevation than the straight-line hike? Or is the elevation calculation wrong? It doesn't look like a 1900' climb is in any way possible but I could be wrong. In any case, it's hard, but the difference between a 114 story building and a 190 is pretty significant.

Admin, would you kindly explain? Thank you!
admin
Site Admin
Posts: 298
Joined: Thu Jul 21, 2011 9:51 am

Re: Route 459287 - Appalachian Trail from Lehigh Gap - Eleva

Post by admin »

There are a couple of reasons why the elevation statistics may appear wrong. One common reason is due to the resolution of the locations sampled for elevation data. Elevation data is not available for all points directly on a road. For routes that are on very hilly terrain, it is likely that an elevation used in the graph is actually off the road and up/down a hill. When that occurs, you may see an up/down section in the graph when in fact the road is flat. For most areas, the sample frequency is sufficient to render reasonably accurate data. But, for a route that is on a hill side, the route can show frequent elevation changes.

The other reason is due to how the elevation statistics are calculated. The up/down values are incremented when a change greater than a threshold has been calculated. If the threshold is too small, insignificant elevation changes (and changes like the ones mentioned above) will be counted in the statistics. If the threshold is too large, some changes in elevation will be “ignored”.

Users can now customize the elevation change threshold on their user profile page. The threshold value is in meters. Elevation changes below the specified threshold are eliminated while calculating the up/down change amounts. You can access the profile page by visiting a Forum page, clicking on “User Control Panel” (upper left of the page), and then clicking on the Profile tab. At the bottom of the profile page, enter a value for the threshold and then submit the form. Once you make the change, the elevation statistics on your “My Routes” page will be calculated using the new threshold value.

For your specific route, whenever you see a jagged elevation line, the elevation up/down values will be incremented if the changes are greater than the threshold value. This can account for the "unexpected" elevation change numbers. Keep in mind that the resolution of the elevation data points affect the elevation change calculation. So, for your specific route, it's possible that you may need a larger threshold value to obtain a better estimate of the up and down elevation changes.
Flagday53 wrote:I volunteer at a local nature facility at the Lehigh Gap. People come in for info and ask about the trails at our location and the Appalachian Trail which is nearby. I traced the AT from the Route 873 parking lot to nearly just over the Lehigh Tunnel of the Pennsylvania Turnpike, just to give people an idea of what a five-mile hike would involve, mostly in terms of elevation changes.

According to the elevation map on the above route, the change is "1900 feet" up and down. From my calculation, the highest point on this route is 1581 and the lowest point is about 440 for a straight-line climb of 1141 feet. The difference between 1900 feet and 1141 feet is 759 feet.

Question: do all the ups and downs on this hike actually add 67% MORE elevation than the straight-line hike? Or is the elevation calculation wrong? It doesn't look like a 1900' climb is in any way possible but I could be wrong. In any case, it's hard, but the difference between a 114 story building and a 190 is pretty significant.

Admin, would you kindly explain? Thank you!
Flagday53
Posts: 2
Joined: Tue Jul 24, 2012 3:31 pm

Re: Route 459287 - Appalachian Trail from Lehigh Gap - Eleva

Post by Flagday53 »

Thank you for your quick response, appreciate it. I'll reset my change level so it's a little greater.

We walked on streets today and the elevation graph does look like a bumpy ride up and down those hills. Again, adding the three uphills from lowest to highest point I come up with 646 feet but the elevation chart says 801. A difference of 155' or 24% more. Over a six mile walk it definitely FELT like 20% more but I doubt that it was.

Do you have a recommendation for a number which will smooth out these calculations? Should I change it to a meter or two meters?

Lish H.
admin
Site Admin
Posts: 298
Joined: Thu Jul 21, 2011 9:51 am

Re: Route 459287 - Appalachian Trail from Lehigh Gap - Eleva

Post by admin »

Unfortunately, there isn't one "right" answer for the threshold value. In your case, there could be included elevation data that is actually off the side of the trail. Increasing the threshold can help filter out some of the points. But, if there are large drop-offs next to your trail and some of the elevation data uses points off your trail, you may not be able to set a threshold which will give you a really good result.
Flagday53 wrote:Thank you for your quick response, appreciate it. I'll reset my change level so it's a little greater.

We walked on streets today and the elevation graph does look like a bumpy ride up and down those hills. Again, adding the three uphills from lowest to highest point I come up with 646 feet but the elevation chart says 801. A difference of 155' or 24% more. Over a six mile walk it definitely FELT like 20% more but I doubt that it was.

Do you have a recommendation for a number which will smooth out these calculations? Should I change it to a meter or two meters?

Lish H.
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