MasterMaps

In my previous blog post we created a grayscale shaded relief (hillshade) from a Digital Elevation Model (DEM). Today, we’ll use the DEM to create color relief and slope shading maps. Color relief or hypsometric tints depict elevation as bands of color, to enhance elevation zones so map readers can better see differences in relief. The colors selected for the tints are assumed to relate to the ground cover typically found at various elevations in the area being mapped. A typical color scheme progresses from dark greens for lower elevations up through yellows/browns, and on to grays and white at the highest elevations. I selected this scheme for my area: Elevation Color 0 900 1300 1900 2500 To create a color relief with gdaldem , we first have to create a text-based color configuration file ( color_relief.txt ), containing the association between elev...

In the first part in this blog series we created a Digital Elevation Model (DEM) for Jotunheimen, a mountainous area in Norway. We’ll use this DEM to create hillshade or shaded relief , a popular cartographic technique to visualise terrain by modulating light and shadows on a map.  GDAL , my favorite GIS Swiss Army Knife, allows you to create hillshade with gdaldem : gdaldem hillshade -of PNG jotunheimen.tif jotunheimen_hillshade.png This command will create this PNG image: [ Download image ] A virtual light source is placed above the DEM to calculate which areas are lightened up and which fall in the shadow. You can clearly see the numerous mountains and valleys. By default, the light source is placed in a top left position (azimuth = 315 degrees). Let’s try to move the light source to a bottom right position (azimuth = 135 degrees): gdaldem hillshade -of PNG -az 135 jotunheimen.tif jotunheimen_hillshade_az135.png [ Download image ] You get the completely...

This is the first post in a new blog series focusing on all the fun you can do with digital terrain data. It’s going to be more related to topographic than thematic mapping, although the two map types can be used in combination. I’ll also try to restrict myself to data and software in the public domain. My focus area is going to be Jotunheimen in Norway, a mountainous area popular among hikers and climbers. The 29 highest mountains in Norway are all in Jotunheimen, including the very highest - Galdhøpiggen (2469 m). Here's a few pictures I took on a hike back in July 2006 which gives you a glimpse of the beautiful landscape: Skogadalen valley and Hurrungane mountain range Fannaråkhytta Bøverbreen glacier It’s many different data formats for storing and working with digital terrain data. I’ll start looking at Digital Elevation Models (DEM) represented as rasters. A raster DEM is a grid of squares or pixels where each square represents an elevation at a geogr...