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The easiest way to determine the percent slope of an area is to measure the
change in height (elevation over a measured distance), then calculate the
percentage of slope. Use the following formula to determine slope:
Rise ÷ Run = Slope %
OR
(Change in elevation ÷ measured distance = slope %)
e.g. 30 metres ¸ 100 metres = .3 or 30%
Calculating a slope steepness index for
a map area
Stages:
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Calculate map area in km˛
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Place 10 X 10 grid overlay over map
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Calculate % slope for each grid square
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Present results as an area average or median slope for the area
(see chart example below)
Slope Angle Index Chart
Transparent grid overlay (11 X 11)
| Slope (%) |
Approximate degrees |
Terminology |
| 0 - 0.5 |
0 |
Level |
| 0.5 - 2 |
0.3 - 1.1 |
Nearly level |
| 2 - 5 |
1.1 - 3 |
Very gentle slope |
| 5 - 9 |
3 - 5 |
Gentle slope |
| 9 - 15 |
5 - 8.5 |
Moderate slope |
| 15 - 30 |
8.5 - 16.5 |
Strong slope |
| 30 - 45 |
16.5 - 24 |
Very strong slope |
| 45 - 70 |
24 - 35 |
Extreme slope |
| 70 - 100 |
35 - 45 |
Steep slope |
| > 100 |
> 45 |
Very steep slope |
Standard slope descriptors
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