Landform Indices

Landform Indices answer a different question from slope and curvature. Instead of measuring a property, they give each cell a label: this is a ridge, this is a valley floor, this is a footslope, this is a pit.

That makes them the bridge between a terrain model and a map somebody can read without being a geomorphologist.

Start here

Geomorphons

The modern reference method, and the one to try first. For each cell it looks out in eight directions, compares the angle up to the horizon with the angle down, and derives a pattern from those comparisons. Ten common patterns cover almost all terrain: flat, peak, ridge, shoulder, spur, slope, hollow, footslope, valley, pit.

Parameter	What to set
Input	Your elevation raster.
Search distance	How far, in cells, to look in each direction. This sets the size of the landforms you detect. Small values find every micro relief, large values find the main structures. The default is 50 cells.
Flatness threshold	The angle, in degrees, below which the ground counts as flat. Raise it if plains come back speckled with spurious slopes.
Flatness distance	An optional distance over which flatness is assessed.
Skip distance	Ignores the first cells around each point, which removes the effect of very local noise.
Output forms	On returns the ten named landforms, off returns the raw ternary patterns. Keep it on.
Output	The classified raster.

Style the result with one distinct colour per class, not with a continuous ramp: the values are categories, and 3 is not between 2 and 4 in any meaningful sense.

Pennock Landform Classification

The classic seven class scheme from Pennock and colleagues, built on the combination of slope, plan curvature and profile curvature. It separates convergent and divergent shoulders, backslopes and footslopes, which is exactly the vocabulary of soil surveys and erosion studies.

Use it when you need to align with that literature. Use Geomorphons when you want the best classification from the data itself.

Relative Topographic Position

Answers “is this cell high or low compared with what is around it”, using the minimum, mean and maximum elevation of a neighbourhood. Simple, fast, and often enough to separate ridges from valleys.

Percent Elev Range is the same idea expressed as a percentage of the local elevation range, and Elev Relative To Min Max compares against the whole raster rather than a neighbourhood.

All the tools

Tool	What it does
Geomorphons	Classifies each cell into ten common landforms from eight direction line of sight patterns.
Pennock Landform Classification	Assigns each cell one of the seven Pennock terrain classes, from slope and curvature.
Multiscale Topographic Position Class	Nine class scheme combining local and broad scale topographic position.
Relative Topographic Position	Position of each cell within its neighbourhood, from the local minimum, mean and maximum.
Percent Elev Range	Local topographic position as a percentage of the neighbourhood elevation range.
Elev Relative To Min Max	Each elevation as a percentage of the whole raster’s elevation range.
Hypsometric Analysis	An area against elevation curve for one or more DEMs, as an HTML report.

Notes

Scale is the parameter. Every tool here depends on the size of the neighbourhood it looks at. A ridge at 50 metres is a slope at 5 kilometres, and neither answer is wrong. Run the tool twice at two scales before deciding.

Classified rasters need categorical styling. See Style to assign one colour per class.