Skip to main content

DEM, DTM and DSM

Elevation terminology is inconsistent internationally, so follow the source metadata rather than assuming DEM always means the same surface.

LINZ usage​

LINZ's national 1 m DEM is the bare-earth product: classified ground returns are gridded to represent terrain with vegetation and buildings removed. Its DSM represents the top surface including vegetation and built features.

OpenTopography usage​

OpenTopography labels the national bare-earth product LINZ1m_DTM and the surface product LINZ1m_DSM. In other words, OpenTopography's DTM corresponds conceptually to LINZ's national bare-earth DEM.

SurfaceLINZ labelOpenTopography national label
bare earthDEMDTM
top surfaceDSMDSM

Which should you use?​

Use terrain/bare earth for:

  • slope and aspect
  • catchment/flow modelling
  • geomorphology
  • landform visualisation
  • contours
  • likely ground profiles

Use DSM for:

  • canopy/building surface
  • rough screening of height above terrain
  • visibility/urban surface context

A canopy-height model is commonly calculated as DSM minus DTM/DEM after ensuring grids align and represent compatible dates.

Water and bridges​

Hydro-flattening and bridge treatment can alter how terrain products represent rivers and crossings. LINZ specifications define processing rules for national products. Inspect the source report when a local hydraulic question depends on those details.

Last reviewed: 26 August 2026

Last updated on