Digital Elevation Model (DEM) consists of point and breakline elevation data, and was originally intended to generate contour lines at 0.5 metre intervals on topographical maps.
Derived from 1:5000 aerial photos, the DEM files represent the ground surface topography to within an accuracy of 15 centimetres vertically and horizontally. Also known as DTM, it is often used in Geographic Information Systems, and is the most common basis for digitally-produced relief maps.
Purchase area-specific DEM mapping products using CITYonline's Map Search Tool
- Use the tool bar tool Draw a Polygon to Digitize an area. Or Use the Select tool to highlight specific layer element, e.g. communities boundaries, etc.
- Click Download> Standard Spatial Data by Polygon or > Custom Spatial Data by Polygon choose Output Data Format and Coordinate system, then Add to Cart.
- Extracting terrain parameters
- Modeling water flow or mass movement (e.g. bank erosion, slides)
- Rendering 3D visualizations
- Creating relief maps
- Creating physical models (including raised-relief maps)
- Rectifying aerial photography or satellite imagery
- Terrain analyses in geomorphology and physical geography
- Accurate – 15 cm accuracy makes DEM products suitable for earthworks and other projects.
- Current – Growth areas are updated annually while established areas are updated on a 3-year cycle; extensive quality control procedures are conducted on an ongoing basis.
- Efficient – Immediate download available; licensing process is completed in minutes, not days.
- Cost effective – Obtaining a DEM map license saves the cost of developing an original.
- Practical – DEM maps are sold on a section basis.
Digital Elevation Model data is collected from 1:5000 scale aerial photography using photogrammetric technology. The data has a positional accuracy of 15 cm in the X, Y, and Z axes. The initial data capture began in 1991. To keep pace with new developments, at least one flight is conducted annually, during which individual sections are checked and updated.
The DEM files, cartographic and ASCII, include points collected on a ten-metre grid, with intermediate points and breaklines added to accurately define the topography.