‹ back to GIS Glossary

Terrain Elevation

Definition

Terrain elevation is the height of the Earth’s surface relative to a vertical datum. In GIS it is represented by digital elevation models (DEMs) derived from LiDAR, photogrammetry, radar, or contour interpolation. Elevation underpins nearly every spatial analysis: it controls drainage directions, viewsheds, radio propagation, temperature lapse rates, and construction feasibility. DEMs can be bare earth (removing vegetation and buildings) or surface models that include canopy and structures. Critical quality dimensions include vertical accuracy, resolution, voids, and artifacts like striping or spikes. Choosing an appropriate datum (orthometric vs ellipsoidal) and consistent units is essential when mixing datasets from different sources.

Application

Engineers compute cut/fill volumes, flood extents, and grades from elevation. Utility planners evaluate line-of-sight for towers. Ecologists model upslope contributing areas and cold-air pooling. Pilots and drone operators rely on terrain for safe flight planning. Elevation also feeds climate and hydrologic models by shaping wind and precipitation patterns.

FAQ

Why does the choice of vertical datum matter in multi-source projects?

Ellipsoidal heights from GNSS and orthometric heights from leveling differ by geoid undulation. Mixing them without conversion creates inconsistent contours and incorrect flood depths; always document and transform datums explicitly.

How do you handle voids or artifacts in radar-derived DEMs?

Fill gaps with auxiliary sources, apply de-striping filters where safe, and validate against checkpoints. For bare earth needs, remove vegetation with ground filtering or use dedicated LiDAR-derived DEMs.

What resolution is appropriate for urban versus regional modeling?

Urban drainage and design often require sub-meter or 1–2 m DEMs, while watershed screening and regional climate work well at 10–30 m. Using finer than necessary increases cost without commensurate benefit.

When should you prefer a surface model over a bare-earth DEM?

For RF propagation, solar on rooftops, or viewshed including buildings and trees, surface models reflect the obstructions that matter to the phenomenon.