Contours

Published Contours

Pre-processed contour line data may be available for the area of interest. For example, the QLD Gov QSpatial 'Contours - 10 metre interval - by area of interest' dataset, downloadable from https://qldspatial.information.qld.gov.au/catalogue/

Extract Contours from DEM files

A DEM file (digital elevation model) contains ground surface point elevation data, as opposed to LiDAR data which contains all survey points (ground, non-ground, vegetation, building, colours etc). DEM files are typically much smaller files and easier to work with than full LiDAR data.

DEM file tiles (1km x 1km) are available for most areas, downloadable from https://elevation.fsdf.org.au/

Contours can be easily extracted from DEM files in QGIS. The process to follow is:

• Download the DEM file tiles (.asc file type) to cover the area required.

• Layer > Add Layer > Add Raster Layer. Select .asc DEMs

• Raster > Miscellaneous > Build Virtual Raster (this is to combine the DEM tiles into a single raster file covering the area required).

• Raster > Extraction > Contour

Extract Contours from LiDAR

Contours can be extracted from LiDAR data, however this can be difficult due to large file sizes and long computer processing times.

LiDAR data may be available for the area of interest, downloadable from https://elevation.fsdf.org.au/

Contours can be extracted from the LiDAR data using a number of tools:

• Using Karttapullautin

• Using the LASTools plugin in QGIS

• Using the LiDAR processing tools built-in OCAD. Contours in OCAD can then be saved in a suitable file format for importing into QGIS.

Styling Contours

A typical style for contours is:

• Rule-based styling, to apply a different style to index and normal contours. See image below. The Rule expression selects indexed contours as those divisible by 25 (i.e. index at 25m) and normal contours shown at 5m increments.

  • Index Contours: 0.25mm stroke width, HTML colour #cf7318

  • Normal Contours: 0.14mm stroke width, HTML colour #cf7318