Slope

Draft: written, not yet checked by a person Operation · slope

The steepness of each cell of an elevation raster, in degrees or percent.

Pitfall. Elevations in feet over a grid in metres, or a grid in degrees, give badly wrong slopes unless the z unit is set.

About this operation
Also called	gradient, steepness, gdaldem slope
Group	`raster/terrain`
Checks	`crs.geographic, raster.nodata`
Pitfalls	1 listed above
Columbus tool	`raster_op · slope`
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`aspect` `hillshade`

Parameters

Name	Type	Required	Default	Values	Note
`z_unit`	enum	yes	Not stated	`m, ft, us-ft`	Unit of the elevation values.
`units`	enum	no	Not stated	`degrees, percent`	Not stated
`band`	integer	no	Not stated	Not stated	Not stated

Inputs and outputs

Direction	Name	Type	Geometry	Note
Input	`raster`	raster	Not stated	An elevation model.
Output	`output`	raster	Not stated	Not stated

In each engine

Engine	Tool	Parameters	Differences
`gdal`	`gdal raster slope`	`z_unit` always crs-units. Elevation is taken in the CRS's horizontal units; otherwise set xscale and yscale (see GDAL's page). `units` → `unit` : degrees = degree; percent = percent `band` → `band` `raster` → `input` `output` → `output`	Cells on the raster's edge are computed from incomplete neighbourhoods; on a uniform slope they come out lower, and differently from PostGIS's. --no-edges leaves them as nodata.
`grass`	`r.slope.aspect`	`z_unit` always crs-units. Elevation is taken in the project's horizontal units; otherwise set zscale. `units` → `format` : degrees = degrees; percent = percent `raster` → `elevation` `output` → `slope`	The same module writes aspect (and curvatures) when those outputs are named; its aspect convention differs from compass bearings unless -n is set.
`postgis-raster`	`st_slope`	`z_unit` always crs-units. Elevation is taken in the CRS's horizontal units; otherwise set scale (see the PostGIS page). `units` → `units` : degrees = DEGREES; percent = PERCENT `band` → `nband` `raster` → `rast`	Cells on the raster's edge are computed from incomplete neighbourhoods; on a uniform slope they come out lower, and differently from GDAL's.
`qgis`	`native:slope`	`z_unit` always crs-units. Elevation is taken in the CRS's horizontal units; otherwise set Z_FACTOR. `units` always degrees `raster` → `INPUT` `output` → `OUTPUT`	None noted
`terra`	`terra::terrain`	`z_unit` always crs-units. Elevation must be in the map units, or metres when the CRS is longitude/latitude. `units` → `unit` : degrees = degrees. not supported: percent. unit is degrees or radians. `raster` → `x`	The same function gives aspect, TPI, TRI, roughness and flow direction (v = "aspect", ...). Preset: `{"v":"slope"}`
`whiteboxtools`	`Slope`	`z_unit` always crs-units. Elevation is taken in the CRS's horizontal units; otherwise set zfactor. `units` → `units` `raster` → `dem` `output` → `output`	None noted
`xarray-spatial`	`xrspatial.slope`	`z_unit` always crs-units. With the default method = 'planar', elevations must be in the same units as the cell size; z_unit applies only with method = 'geodesic'. `units` always degrees `raster` → `agg`	Takes an xarray DataArray with x and y coordinates; edge cells are NaN by default (boundary = 'nan').