D8 Flow Direction
Chooses one of eight neighboring cells with the steepest downward slope.
si=(zc−zi)/di
Direction = argmaxi si
Best used when: a single-direction grid drainage model is appropriate.
Flow Direction
Calculate the downslope flow direction from each DEM cell, typically using an eight-neighbor (D8) grid.
HydrologyEnd-User DocumentationTheory + Formula + Parameters1. What This Feature Does
Calculate the downslope flow direction from each DEM cell, typically using an eight-neighbor (D8) grid.
Cloud workflow: choose data → configure the scientific method → run → review the resulting layer/report. No programming is required.
2. Recommended Workflow
Choose DEM/elevation band.
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Fill sinks first if required.
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Compute direction to the steepest downslope neighbor.
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Use the direction raster for accumulation/watershed analysis.
3. Theory, Methods & Equations
4. Input Data
| Input | Type | Requirement | Description |
|---|---|---|---|
| DEM Raster | raster | Required |
5. Parameters Available in the Application
| Parameter | Default | Choices / Range | How to Use It |
|---|---|---|---|
| Elevation Band | — | — | |
| Fill Sinks First | On | — |
6. Output & Interpretation
The result should be interpreted according to the selected method and the physical meaning of the input data. Preserve source units, coordinate reference information, NoData meaning, acquisition date, and preprocessing level when comparing results.
Scientific interpretation: an algorithm can produce a numerically valid result even when the input data are unsuitable. Always check masks, units, sensor characteristics, spatial resolution and reference data.
7. Best Practices
- Use analysis-ready inputs and remove invalid/cloud/noise artifacts that are not part of the target phenomenon.
- Choose parameters from the physical scale of the data, not only from visual appearance.
- Keep categorical and continuous rasters conceptually separate when selecting interpolation/resampling methods.
- Compare the result with the source image and independent reference information.
- Document the settings used when results will be compared across dates, sensors or study areas.