From DEM to Decision: A Terrain Analysis Workflow for Site Suitability

Site suitability analysis lives or dies on the quality of the underlying terrain analysis. Here's the workflow we actually use, from raw DEM to a defensible recommendation.

Step 1: DEM Preprocessing

Before any analysis, we fill sinks and correct flow-disrupting artifacts (a common issue in SRTM and other freely available DEMs), and resample to a resolution appropriate for the site scale — over-resolving a coarse-source DEM creates false precision, not better answers.

Step 2: Derived Terrain Surfaces

From the conditioned DEM we derive slope, aspect, curvature, and — where relevant — a topographic wetness index, each of which becomes an input layer to the suitability model rather than an end product in itself.

Step 3: Hydrological Conditioning

For sites where drainage matters (which is most sites), we derive flow accumulation and stream networks, and apply buffer or exclusion criteria around watercourses per the relevant regulatory setback requirements.

Step 4: Multi-Criteria Weighted Overlay

Individual criteria — slope suitability, proximity to infrastructure, flood exclusion zones, soil suitability — are normalized to a common scale and combined via a weighted overlay, with weights set collaboratively with the client rather than assumed unilaterally by us.

Step 5: Sensitivity Testing

We always test how sensitive the final suitability ranking is to reasonable variation in the weighting scheme — if a site's ranking flips under a modestly different but equally defensible weighting, that's a finding worth reporting, not hiding.

Why This Matters

A suitability map that skips straight from raw DEM to colored overlay, without transparent intermediate steps and sensitivity testing, might look identical to a rigorous one — but it won't survive scrutiny from a funding body, regulator, or opposing technical reviewer. The workflow discipline is the actual deliverable, not just the final map.