Below you will find a few tips on working with DEM models in Qgis. Image taken from http://earthexplorer.usgs.gov/ of Big Island Hawaii
You download your GeoTiff file and it looks like this:
To fix it right click on the layer>properties>Style Tab. Under contrast enhancement choose StretchtoMinMax
It should look like this:
Still not much but better. This is an image of The Big Island Hawaii . The lighter the color the higher to elevation and the darker the color the lower. Since this is an island the dark is water in this case
Let’s run a few raster analysis tools to learn more about it.
First let’s calculate slope. You can either express slope as a percent or as is. If you have issues when creating your raster analysis and it comes out looking much like a tv screen with static you need to convert the unit of the layer to the units of the map. If you map is in meters then it is 111120. If it is in feet 370400. It is input whenever you see this box here:
Slope as a percent:
For this exercise I used a scale of 111120 to convert it to meters
Next we can add contours to the map:
When choosing an interval be careful. It is going to generate a line shapefile that can be very large so just play around and see what work for your project and make sure to include it somewhere on the map or you can label the contour lines also.
I used 100 meter intervals to create this map. I also turned off the layers so it can be seen better
These are just a few of the tools available in Qgis. Feel free to leave a comment requesting help or any other tutorials.