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Ben Strege  
#1 Posted : Thursday, February 13, 2020 3:04:12 PM(UTC)
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I have received a few questions about the hilliness index that is shown for the portages. I am trying to find a good spot to put the explanation on the map, but it is a long explanation... so I'll put it here first while I find a place for it.

The elevation graphs show the elevation every two rods (the elevation might be an estimate from the USGS or the Canadian equivalent, but it seems to be pretty detailed). I then look at every 2-rod segment (2 rods = 10 meters) and determine if it is going up or down. I separately add up all of the "up" segments and the "down" segments. These two figures are not netted. I add up the two figures to get a total elevation change along the portage (again, at 2-rod intervals).

For example, if a portage goes up 30 meters and then descends 30 meters, the net would be zero. The net figure doesn't show how "hilly" the portage is. So instead I say it climbed 30 meters and descended 30 meters for a total elevation change of 60 meters. The same result would come out if the portage rose 15 meters, descended 15 meters, rose 15 meters, and descended 15 meters again.

The elevation change is divided by the length of the portage (the rods are converted to meters). If two portages have the same elevation change, the shorter one will be "hillier" than the longer one. For example, if the portage above is 100 rods (503 meters) long, the index will be 60/503 = 0.1193. If it is 200 rods long, it will 60/1006 = 0.0596. The 100-rod portage would be one of the steeper portages (that index is pretty high) while the 200-rod one is about average.

Finally, I multiply the index by 1,000 just to make it more readable. So the 100-rod one would be 119.3 and the 200-rod one 59.6.

Granted, the hilliness index does not make every portage comparable. For example, if the portage was completely flat except for a 60 meter cliff, it would still show the same hilliness index as above. Using the index and the graph together, though, should give you a pretty good idea of it.

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