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 slope

Slope is one of the most basic parameters that can be derived from a DEM. It corresponds to the first derivative of the DEM, and it represents the rate of change of the elevation. It is computed by analyzing the elevation of each cell and comparing this with the elevation of the surrounding ones. This recipe shows you how to compute slope in QGIS.

Getting ready

Open the DEM that we prepared in the previous recipe.

How to do it…

  1. In the Processing Toolbox option, find the Slope algorithm and double-click on it to open it:

  2. Select the DEM in the Input layer field.

  3. Click on Run to run the algorithm.

The slope layer will be added to the QGIS project.

How it works…

Slope is calculated from a DEM elevation model by analyzing the cells around a given one. This analysis is performed by the slope algorithm from the GDAL library.

There's more…

There are several ways of using the slope algorithms in QGIS. Here are some comments and ideas about this.

Using a ratio for elevation values

If the units...