Datenpaket: Terrain Slope of Bavaria

The map of terrain slope is based on the Digital Terrain Model of Bavaria with a spatial resolution of 5 m (DGM5) and characterizes the inclination of the actual terrain surface. Terrain slope was calculated
according to Horn (1981), considering the eight immediately adjacent raster cells, and is expressed in degrees (°). The method determines local terrain inclination based on elevation differences within a
3 × 3 cell neighborhood. The DGM5 was used in its original terrain geometry. Consequently, both natural and anthropogenic terrain features, such as embankments, dams, or cuttings, may influence the derived slope values.
The dataset provides a comprehensive description of topographic conditions and enables the spatial differentiation of terrain areas with different degrees of inclination.

This dataset provides a Bavaria-wide representation of terrain slope derived from the Digital Terrain Model of Bavaria (DGM5) at 5 m spatial resolution.
Terrain slope describes the local inclination of the terrain surface relative to the horizontal plane. It was calculated according to Horn (1981), using elevation differences within a 3 × 3 raster-cell neighbourhood comprising the eight cells immediately adjacent to each central raster cell.
Slope is expressed in degrees (°), with 0° representing a horizontal terrain surface and increasing values indicating increasing terrain steepness. The theoretical range extends from 0° to 90°.
The DGM5 used as input is a preprocessed digital terrain model. No additional hydrological conditioning was applied prior to the calculation of terrain slope. In particular, the terrain was not modified specifically to enforce hydrological connectivity or drainage patterns for the purpose of this analysis.
Consequently, the resulting slope values characterize the local inclination of the terrain surface represented in the DGM5 rather than a hydrologically conditioned terrain surface. Terrain structures represented in the DGM5, including anthropogenic features such as embankments, dams, cuttings, or other artificial modifications of the terrain, may therefore influence the calculated slope values.
The dataset provides a spatially comprehensive characterization of terrain inclination across Bavaria and enables the spatial differentiation of areas with different degrees of terrain steepness. It can support agricultural, forestry, ecological, climatological, geomorphological, landscape, and other environmental analyses.

INPUT DATA
Digital Terrain Model of Bavaria (DGM5)
• Spatial resolution: 5 m
• Data provider: Bavarian Surveying Administration / Bayerische Vermessungsverwaltung
• Product: Digitales Geländemodell 5 m (DGM5)
• License: CC BY 4.0
• Source: Open Data Bayern

DATASET SPECIFICATIONS
• Spatial extent: Bavaria, Germany
• Spatial resolution: 5 m
• Unit: degrees (°)
• Variable: terrain slope
• Data type: raster
• File format: GeoTIFF / Cloud Optimized GeoTIFF (COG)
• Coordinate reference system: ETRS89 / UTM zone 32N
• EPSG: 25832

PROCESSING
Input: Digital Terrain Model of Bavaria (DGM5), 5 m spatial resolution.
Method: Terrain slope was calculated according to Horn (1981).

The local inclination of the terrain surface is derived from elevation differences within a 3 × 3 raster-cell neighbourhood. The eight cells immediately adjacent to each central raster cell are considered in the calculation.
The resulting slope represents the magnitude of the local terrain gradient and is expressed as an inclination angle in degrees relative to the horizontal plane.

Processing environment
• Software environment: R
• Package: terra
• Function: terrain()
• Processing platform: terrabyte

The DGM5 used as input is a preprocessed digital terrain model. No additional hydrological conditioning of the terrain was applied prior to slope calculation.
The derived slope values therefore represent the local inclination of the terrain geometry contained in the DGM5 rather than that of a hydrologically conditioned terrain representation. Anthropogenic terrain structures represented in the DGM5 may consequently influence the calculated slope values.

PARAMETER SETTINGS
• Function: terra::terrain()
• Variable: v = "slope"
• Output unit: unit = "degrees"
• Neighbours: neighbors = 8
• Neighbourhood: 3 × 3 raster cells
• Raster cell size: 5 m
• Algorithm: Horn (1981)

The slope calculation is based on elevation differences within the immediate 3 × 3 cell neighborhood. At a raster resolution of 5 m, the calculated values therefore characterize local terrain inclination at the spatial scale represented by the DGM5.

VALUE INTERPRETATION
Slope values represent the angle of inclination of the terrain surface relative to the horizontal plane: 0° - horizontal terrain surface, Increasing values: increasing terrain steepness, 90° - theoretical maximum corresponding to a vertical surface

The theoretical range of the dataset is therefore 0° to 90°.
Slope expressed in degrees should not be confused with slope expressed as percent gradient. Conversion between degrees and percent slope is nonlinear.

INTERPRETATION AND LIMITATIONS
The dataset represents the local geometric inclination of the terrain surface represented in the DGM5 and should be interpreted accordingly.
In particular:
• The slope calculation is derived from the terrain geometry represented in the DGM5.
• The input DGM5 is a preprocessed digital terrain model.
• No additional hydrological conditioning was performed specifically for the slope calculation.
• The dataset therefore does not represent slope derived from a hydrologically conditioned terrain model.
• Anthropogenic terrain structures represented in the DGM5, including embankments, dams, cuttings, and similar features, may influence local slope values.
• Slope is calculated locally from the immediate 3 × 3 raster-cell neighbourhood and therefore reflects terrain inclination at the spatial scale represented by the 5 m DGM5.
• Local slope values depend on the spatial resolution and properties of the underlying elevation model and should therefore not be interpreted independently of the 5 m raster resolution.
• The dataset describes terrain geometry and does not by itself provide information on hydrological connectivity, surface runoff, erosion processes, or currently active geomorphological processes.

RECOMMENDED USE
The dataset can be used as a terrain-related spatial variable in regional and Bavaria-wide analyses, such as characterization of terrain steepness and topographic conditions, agricultural and forestry analyses, and ecological and biodiversity modelling.
Slope can be an important terrain-related input variable for analyses of runoff, erosion, soil moisture, or other hydrological and geomorphological processes. However, the slope dataset itself does not represent these processes or hydrological connectivity.
For applications requiring explicit representation of surface runoff, drainage networks, flow accumulation, or hydrological connectivity, hydrologically conditioned elevation data and dedicated hydrological terrain derivatives should be used instead.

REFERENCE
Horn, B. K. P. (1981). Hill shading and the reflectance map. Proceedings of the IEEE, 69(1), 14–47.

DATA SOURCE
Digitales Geländemodell 5 m (DGM5), Bavarian Surveying Administration / Bayerische Vermessungsverwaltung, Open Data Bayern, licensed under CC BY 4.0.