Flow routing and accumulation
The D8 algorithm assigns flow to one of eight neighbouring raster cells. A hydrologically conditioned surface supports routing, while the original elevations remain distinct.
Accumulation counts contributing cells including the cell itself. A catchment represents contributions within the selected analysis extent; unknown upstream areas can remain outside it.
Depressions and boundary crossings
Differences between original and conditioned heights describe relative terrain depressions, not predicted water depth. A boundary crossing describes the model extent, not a physical drain.
Missing cells, clipped context, source date and raster spacing affect the result. A locally complete classification does not establish catchment completeness beyond the study area.
Bounded computation and visible units
The established resource contract limits an analysis to four million cells and one bounded raster worker. Excessive requests are rejected rather than silently lowering resolution.
Each region and product must disclose actual grid spacing, cell area, distance and elevation units, vertical datum and source version. A finer raster is not proof of greater vertical accuracy.
Check the location before starting
The US pilot accepts user-drawn study areas within the contiguous-US pilot extent. The worker checks for usable native USGS project-level 1 m elevation data. Coverage is incomplete and may fail for a selected area; no coarser dataset is silently substituted.
Baden-Württemberg remains a separate established German workflow with official ALKIS parcels. US address points and drawn areas are not official parcel boundaries.
What terrain screening cannot determine
Terrain screening does not simulate rainfall, infiltration, sewer capacity or the hydraulic effects of walls and culverts. It cannot predict flood depth, size a drainage system or confirm that a property is safe to build on.
A local catchment is limited to the analysed area. Contributions from beyond its boundary can be unknown. A modelled boundary crossing is not evidence of a real drain or drainage outlet.
Common questions
Does this predict flooding?
No. The screening describes terrain and potential surface flow paths. It does not simulate a storm or predict water levels.
Are PDF reports free?
No. PDFs are paid products. A free preview or analysis access key is not a purchase. Check the pricing page for current sales availability.
Editorial: Terraincheck · Updated 6 November 2026. See our methodology · data sources.
Terrain screening provides preliminary context. Site assessment, engineering design and construction decisions require appropriately qualified professionals.