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
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
Index

Automating analysis tasks using the graphical modeler


Most analysis tasks involve using several algorithms. Repeating the same analysis with a different dataset or different input parameters requires using them one by one, making this task tedious and error-prone. You can automate analysis workflows using the Processing graphical modeler, which allows you to define a workflow graphically and wrap it in a single algorithm. This recipe introduces the main ideas about the modeler and creates a simple model as an example.

Getting ready

No special preparation is needed in QGIS for this recipe, but make sure that you have read the previous recipe about computing a topographic index. This recipe will create a model based on the workflow in that recipe, so it is important that you understand it.

How to do it…

  1. Open the graphical modeler by navigating to Processing | Graphical modeler:

  2. Double-click on the Raster Layer item to add a raster input. In the dialog that will appear to define the input, name...