Enhanced Digital Terrain Model height data

An Enhanced Digital Terrain Model (DTM) is a digital file consisting of break-lines and spot heights providing a highly detailed representation of the topographical variations in the Earth's surface.

Break-lines show dramatic change in slope for example cliffs, road embankments.

How often is the data updated?

Enhanced DTMs are updated within the same cycle as the orthophotography:

Key features

  • the enhanced DTM consists of a point file of heights, along with break-lines showing dramatic changes in height
  • spot heights are on average 60m apart although the enhanced DTM carries a higher density of data where it is most needed
  • can be used in the digital creation of 3D mapping such as slope and aspect maps
  • using Geographical Information software, orthophotographs and maps can be draped over a Triangular Irregular Network (TIN) derived from a DTM to create a 3D view of the land surface
  • DTM data can also be used in a GI software to create thematic maps, grids and contours
  • the enhanced DTM can be used in the electronic process of representing topography in three dimensions for example in a Geographical Information or CAD system.
  • the enhanced DTM is Land & Property Service’s most detailed height product


  • planning
  • engineering
  • visualisation
  • height analysis
  • environmental impact analysis
  • sight lines
  • wind flow and pollution dispersion
  • soil erosion modelling
  • flow direction and accumulation
  • watershed delineation

Technical information

  • the DTM is created from stereo imagery in the orthophotography production process
  • text format
  • all height measurements refer to elevation in metres above mean sea level at Belfast Lough
  • enhanced DTMs can be used to generate 3D Triangular Irregular Networks (TIN)
  • the DTM has an accuracy of 1.0m RMSE (root means square error) - 65 per cent of data has an accuracy of 1.0m, 90 per cent has an accuracy of 2.0m, and 99 per cent of the data has an accuracy of 3.0m

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