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in 3D. Spatial & Terrain Analysis. Nigel Trodd Coventry University. Aim & objectives. To understand the application of 2D+ terrain analysis in GIS. to review methods of 2D spatial analysis to identify 1st and 2nd order derivatives of DEM data

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spatial terrain analysis

in 3D

Spatial & Terrain Analysis

Nigel Trodd

Coventry University

aim objectives
Aim & objectives
  • To understand the application of 2D+ terrain analysis in GIS
  • to review methods of 2D spatial analysis
  • to identify 1st and 2nd order derivatives of DEM data
  • to identify advanced methods of terrain analysis


… improves communication & interaction

… is essential for environmental modelling

… drives new methods of data capture & management


we should not rush these things

without some basic




points, lines, areas



  • 2D
  • 3D
  • 2.5D

Data modelling



spatial concept

not a problem

2D + above, below

DEM, TIN, voxel

measurement of inherent properties
Measurement of inherent properties
  • simple geometric measurements associated with objects

Point – none!

Line - length, mid-point

Area - perimeter, area, centroid, shape

Surface – mean, min, max, range, variance

Volume – volume, centroid

definition of spatial analysis
Definition of spatial analysis
  • A method of analysis is spatial if the results depend on the locations of the objects being analyzed


    • move the objects and the results change


    • the analysis modifies geometry or creates new geometry
spatial operators
Spatial operators

Berry, J.K., 1987, Fundamental operations in computer-assisted map analysis, International Journal of GIS1 119-36.

  • Reclassifying maps
  • Overlaying maps
  • Proximity and connectivity
  • Characterizing neighbourhoods
  • Change or create a new entity using spatial properties

Reclassify & then merge adjacent areas with the same attribute i.e. change geometry

overlay analysis
Overlay analysis
  • Point in Polygon
  • Polygon on Polygon
proximity analysis buffering
Proximity analysis: buffering
  • Create a new area within a user-defined distance of an existing entity

e.g., to determine areas impacted by a proposed highway

contiguity analysis
Contiguity analysis

Which states share a border with Missouri?

neighbourhood analysis
Neighbourhood analysis
  • Local operators calculate an output value based on the values of nearby locations
  • Zonal operators
  • Focal operators
  • the area(s) of interest is defined by another data layer
  • the area of interest is defined by a user-specified moving window

Focal operators

output at a location calculated from the values at locations in a window

terrain analysis
Terrain analysis

DEM visualisations


1st order derivative

2nd order derivative

in 2.5D

summary conclusion
Summary & Conclusion
  • 3D GIS is appealing - but rarely implemented
  • 2.5D is frequently implemented using a surface entity type
  • Terrain analysis in 2.5D exploits multiple visualisations of a DEM and its’ 1st and 2nd order derivatives
  • 2.5D products make useful inputs to environmental models
  • Much (most?) terrain analysis still relies on spatial operations in 2D