Use QGIS to generate contour lines from a DEM

This guide will help those who have used ESRI software in the past to create countour line datasets.  Instead of spending big bucks on ArcDesktop and the Spatial Analyst you can do this for free with QGIS.

The first step is to load your DEM data.  QGIS uses GDAL to handle raster datasets, and GDAL can load almost every format out there.  Seriously, GDAL is awesome.  Once you have loaded your data make sure it is in the correct projection by right clicking the layer in the table of contents, the select Set Layer CRS.  You’ll also want to set the project to your layer’s CRS, you can either use the Set Project to Layer CRS in the same menu, or go to File, Project Properties, and click the Coordinate Reference System tab.

In other GIS software your DEM may automatically be drawn with a grayscale or colormap already set.  In QGIS by default you’ll only see a gray rectangle.

QGIS displaying a DEM with no colormap or grayscale stretching.

On the style tab of the layer properties menu you can select how you want your raster to be symbolized.  Here’s the same layer displayed with elevations represented by pseudocolors:

DEM displayed with pseudocolors

To generate contours click Raster, then Extraction, then select the Contour menu.

QGIS contour menu.

The menu is pretty self explanatory.  It is a front end for the gdal_contour command line tool.  You can use the generated command at the bottom as the starting point for a batch file if you have several files you need to convert.

Contour lines sitting on DEM they were created from

Easy peasy!

2012

07/14

POSTED BY

Phil

CATEGORY

OSGeo
QGIS

TAGS

Contour lines
DEM
GDAL
OSGeo
QGIS

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