Book Image

QGIS 2 Cookbook

By : Alex Mandel, Víctor Olaya Ferrero, Anita Graser, Alexander Bruy
Book Image

QGIS 2 Cookbook

By: Alex Mandel, Víctor Olaya Ferrero, Anita Graser, Alexander Bruy

Overview of this book

QGIS is a user-friendly, cross-platform desktop geographic information system used to make maps and analyze spatial data. QGIS allows users to understand, question, interpret, and visualize spatial data in many ways that reveal relationships, patterns, and trends in the form of maps. This book is a collection of simple to advanced techniques that are needed in everyday geospatial work, and shows how to accomplish them with QGIS. You will begin by understanding the different types of data management techniques, as well as how data exploration works. You will then learn how to perform classic vector and raster analysis with QGIS, apart from creating time-based visualizations. Finally, you will learn how to create interactive and visually appealing maps with custom cartography. By the end of this book, you will have all the necessary knowledge to handle spatial data management, exploration, and visualization tasks in QGIS.
Table of Contents (19 chapters)
QGIS 2 Cookbook
About the Authors
About the Reviewers

Calculating a topographic index

As the topography defines and influences most of the processes that take place in a given terrain, the DEM can be used to extract many different parameters, which give us information about these processes. This recipe shows you how to calculate a popular one, which is called the Topographic wetness index, which estimates the soil wetness based on the topography.

Getting ready

Open the DEM that we prepared in the Preparing elevation data recipe.

How to do it…

  1. Calculate a slope layer using the Slope, aspect, curvature algorithm from SAGA in the Processing Toolbox option. Calculate a catchment area layer using the Catchment area algorithm from the Processing Toolbox option. Note that you must use a sink-less DEM, such as the one that we generated in the previous recipe with the Fill sinks algorithm.

    Open the Topographic wetness index algorithm from the Processing Toolbox option and fill it in, as shown in the following screenshot:

  2. Run the algorithm. This will create...