Distance Between Topo/Contour Lines
I understand how to calculate the elevation at a point between two contour lines when the dimensions and contour elevations are given using Rise / Run = Distance A / Total Distance
So using an example from Designer Hacks:
X / 8′ = 10’ / 18′
X = 8 x 10 / 18
X = 4.44′ = Elev. 824.44'
But how do you calculate the dimension or max distance between two contour lines if the elevations and a slope percentage are given? Is the formula Rise / Run = Slope? So Rise / X = Slope and solve for X ?
Thanks

If I'm understanding what youre asking  sometimes it helps to think of a percent grade or slope as "something over 100".
If they had said it's a 55.5% grade  that's 55.5/100, which is the same thing as 10/18. From knowing that, you'd plug in numbers exactly the same way as your example. 55.5/10 x 8 = 4.44.........so 824.44
It also helps to sketch a right triangle, and fill in the knowns  a little trig keeps things straight.

Thanks Kurt! That's helpful. Pluralsight also suggested the following formulas.
S = DE / L and S x L = DE
Where S=Slope, L=Total Length, DE=Depth (i.e. elevation change).
So for the above example.
S = 10' / 18' = 0.555 (or 55.5% slope)
0.555 x 8' = DE = 4.44'
So the elevation at the point is 820' + 4.44' = 824.44'
If the slope and elevation change are given and we needed to find the distance between the contours we could use the first equation and solve for the length. So 0.555 = 10' / L = 18'
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