Terrain analysis extracts meaning from elevation models. First derivatives give slope (steepness) and aspect (facing direction); second derivatives give curvature; visibility algorithms compute what can be seen from where. These simple-sounding products drive serious decisions: construction feasibility, landslide susceptibility, solar and wind siting, telecom line-of-sight, visual impact of developments, and military terrain assessment.
Slope, aspect and curvature
Slope is the workhorse: agriculture, construction standards, erosion models and hazard mapping all classify the world by steepness. Aspect controls sun and moisture — vineyard sites, snow persistence, solar yield. Curvature identifies ridges, channels and hollows, shaping water flow and soil accumulation.
All inherit the DEM’s character: resolution and surface type (DTM versus DSM) change results materially, and derivative noise amplifies elevation noise — smoothing choices are analytical decisions, not cosmetics.
Visibility: viewsheds and line of sight
A viewshed marks every cell visible from an observer, honouring terrain (and, with a DSM, buildings and trees), observer and target heights, and range limits. Line-of-sight profiles test single sight-lines with obstruction locations identified.
Applications span telecom link planning, wind-farm and quarry visual impact, surveillance and fire-tower placement, scenic-resource protection — and the same mathematics in defence terrain analysis.
Composed terrain products
Real deliverables compose primitives: developable-land maps (slope + aspect + hazard overlays), cut–fill balances between design surfaces and existing ground, terrain ruggedness and mobility classifications, solar irradiation maps integrating slope, aspect and horizon shading.
As always, fitness demands matching the DEM to the question: parcel-scale earthworks want centimetre LiDAR terrain, regional siting tolerates coarser sources.
Frequently asked questions
Should viewshed analysis use a DTM or DSM?
For realistic visibility among buildings and trees, a DSM (or DTM plus modelled obstructions); bare-earth viewsheds systematically overstate what is visible in built and forested landscapes.
How does DEM resolution affect slope analysis?
Coarser DEMs smooth terrain and understate slopes, especially in dissected landscapes; finer DEMs capture true steepness but also more noise. Choose resolution to match the terrain features that matter to the decision.
Related topics
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