Learning QGIS - Third Edition

Table of Contents

Learning QGIS Third Edition

Credits

About the Author

About the Reviewer

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Why subscribe?

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Errata

Piracy

Questions

1. Getting Started with QGIS

Installing QGIS

Installing QGIS on Windows

Installing on Ubuntu

Running QGIS for the first time

Introducing the QGIS user interface

Finding help and reporting issues

Summary

2. Viewing Spatial Data

Loading vector data from files

Dealing with coordinate reference systems

Loading raster files

Georeferencing raster maps

Loading data from databases

Loading data from OGC web services

Styling raster layers

Styling vector layers

Creating point styles – an example of an airport style

Creating line styles – an example of river or road styles

Creating polygon styles – an example of a landmass style

Loading background maps

Dealing with project files

Summary

3. Data Creation and Editing

Creating new vector layers

Working with feature selection tools

Selecting features with the mouse

Selecting features with expressions

Selecting features using spatial queries

Editing vector geometries

Using basic digitizing tools

Using advanced digitizing tools

Using snapping to enable topologically correct editing

Using measuring tools

Editing attributes

Editing attributes in the attribute table

Editing attributes in the feature form

Creating a feature form using autogenerate

Designing a feature form using drag and drop designer

Designing a feature form using a .ui file

Calculating new attribute values

Reprojecting and converting vector and raster data

Joining tabular data

Setting up a join in Layer Properties

Checking join results in the attribute table

Using temporary scratch layers

Checking for topological errors and fixing them

Finding errors with the Topology Checker

Fixing invalid geometry errors

Adding data to spatial databases

Summary

4. Spatial Analysis

Analyzing raster data

Clipping rasters

Analyzing elevation/terrain data

Using the raster calculator

Combining raster and vector data

Converting between rasters and vectors

Accessing raster and vector layer statistics

Computing zonal statistics

Creating a heatmap from points

Vector and raster analysis with Processing

Finding nearest neighbors

Converting between points, lines, and polygons

Identifying features in the proximity of other features

Sampling a raster at point locations

Mapping density with hexagonal grids

Calculating area shares within a region

Batch-processing multiple datasets

Automated geoprocessing with the graphical modeler

Documenting and sharing models

Leveraging the power of spatial databases

Selecting by location in SpatiaLite

Aggregating data in SpatiaLite

Summary

5. Creating Great Maps

Advanced vector styling

Creating a graduated style

Creating and using color ramps

Using categorized styles for nominal data

Creating a rule-based style for road layers

Creating data-defined symbology

Creating a dynamic heatmap style

Creating a 2.5D style

Adding live layer effects

Working with different styles

Labeling

Customizing label text styles

Controlling label formatting

Configuring label buffers, background, and shadows

Controlling label placement

Configuring point labels

Configuring line labels

Configuring polygon labels

Placing labels manually

Controlling label rendering

Designing print maps

Creating a basic map

Adding a scalebar

Adding a North arrow image

Adding a legend

Adding explanatory text to the map

Adding map grids and frames

Creating overview maps

Adding more details with attribute tables and HTML frames

Creating a map series using the Atlas feature

Presenting your maps online

Exporting a web map

Creating map tiles

Exporting a 3D web map

Summary

6. Extending QGIS with Python

Adding functionality using actions

Configuring your first Python action

Opening files using actions

Opening a web browser using actions

Getting to know the Python Console

Loading and exploring datasets

Styling layers

Filtering data

Creating a memory layer

Exporting map images

Creating custom geoprocessing scripts using Python

Writing your first Processing script

Writing a script with vector layer output

Visualizing the script progress

Developing your first plugin

Creating the plugin template with Plugin Builder

Customizing the plugin GUI

Implementing plugin functionality

Creating a custom map tool

Summary

Index

Learning QGIS Third Edition

Learning QGIS Third Edition

Copyright © 2016 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: September 2013

Second edition: December 2014

Third edition: March 2016

Production reference: 1030316

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham B3 2PB, UK.

ISBN 978-1-78588-033-9

www.packtpub.com

Credits

Author

Anita Graser

Reviewer

Cornelius Roth

Commissioning Editor

Veena Pagare

Acquisition Editor

Larissa Pinto

Content Development Editor

Prashanth G. Rao

Technical Editor

Tanmayee Patil

Copy Editor

Vikrant Phadke

Project Coordinator

Bijal Patel

Proofreader

Safis Editing

Indexer

Mariammal Chettiyar

Production Coordinator

Arvindkumar Gupta

Cover Work

Arvindkumar Gupta

About the Author

Anita Graser studied geomatics at the University of Applied Sciences Wiener Neustadt, Austria, from where she graduated with a master's degree in 2010. During her studies, she gained hands-on experience in the fields of geo-marketing and transportation research. Since 2007, she has been working as a geographic information systems (GIS) expert with the dynamic transportation systems group at the Austrian Institute of Technology (AIT), where she focuses on analyzing and visualizing spatio-temporal data. Anita serves on the OSGeo board of directors and the QGIS project steering committee. She has been working with GIS since 2005, provides QGIS training courses, and writes a popular blog on open source GIS at anitagraser.com.

I would like to say thanks to my family, partner, and coworkers for their support and encouragement. Of course, I also want to thank the whole QGIS community for their continued efforts to provide the best open source GIS experience possible and everyone who made the previous editions of Learning QGIS such great successes.

About the Reviewer

Cornelius Roth holds a master's degree in geography and geoinformatics at the University of Salzburg. He is currently working at the Department of Geoinformatics on research projects, helping them use GIS-related methods in emergency and air traffic management, open source GIS, and open data.

Recently, he has also worked at the economic development agency BGL, Bavaria, with a strong focus on fostering companies when applying GIS methods and services to support their business objectives. As a third pillar, Cornelius manages e-learning courses for the UNIGIS distance learning network in Salzburg.

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Preface

Welcome to the third edition of Learning QGIS. This book aims to introduce you to QGIS 2.14 and show you how to perform core geospatial tasks using this popular open source GIS. It takes you through six chapters from QGIS installation and setup in the first chapter, to the essentials of viewing spatial data in the second chapter. The third chapter covers data creation and editing, followed by the fourth chapter, which offers an introduction to performing spatial analysis in QGIS. In the fifth chapter, you will learn how to create great maps and how to prepare them for print, and the final chapter shows you how you can extend QGIS using the Python scripting language.

What this book covers

Chapter 1, Getting Started with QGIS, covers the installation and configuration of QGIS. We will also see the user interface and how to customize it. By the end of this chapter, you will have QGIS running on your machine and be ready to start with the tutorials.

Chapter 2, Viewing Spatial Data, covers how to view spatial data from different data sources. QGIS supports many file and database formats as well as OGC web services. We will first see how we can load layers from these different data sources. Then, we will look into the basics of styling both vector and raster layers and will create our first map. We will finish this chapter with an example for loading background maps from online services.

Chapter 3, Data Creation and Editing, covers how to create and manipulate spatial datasets. We will cover how to select features and take measurements before we continue with editing feature geometries and attributes. We will then reproject vector and raster data and learn how to convert between different file formats. Furthermore, we will join data from text files and spreadsheets to our spatial data. We will also explore the use of temporary scratch layers, learn how to fix common topological errors, and finally, how to load data into spatial databases.

Chapter 4, Spatial Analysis, covers raster processing and analyses tasks such as clipping and terrain analysis. Then we cover converting between raster and vector formats before we continue with common vector geoprocessing tasks such as generating heatmaps and calculating area shares within a region. Finally, we will finish the chapter with exercises in automating geoprocessing workflows using the QGIS Processing modeler and leveraging the power of spatial databases for analysis.

Chapter 5, Creating Great Maps, covers important features that enable us to create great maps. We will go into advanced vector styling, building on what we learned in Chapter 2, Viewing Spatial Data. Then, we will cover labeling using examples of labeling point locations as well as creating more advanced road labels with road shield graphics. We will also cover how to tweak labels manually. We will get to know the print composer and how to use it to create printable maps and map books. Finally, we will cover solutions to present your maps on the Web.

Chapter 6, Extending QGIS with Python, covers scripting QGIS with Python. We will start with an introduction to actions before we get started with the QGIS Python Console and more advanced development of custom tools for the Processing toolbox. Finally, we will cover how to create our own plugins.

What you need for this book

To follow the exercises in this book, you need QGIS 2.14. QGIS installation is covered in the first chapter and download links for the exercise data are provided in the respective chapters.

Who this book is for

If you are a user, developer, or consultant and want to know how to use QGIS to achieve the results you are used to from other GIS, this is the book for you. This book is not intended to be a GIS textbook. You, the reader, are expected to be comfortable with core GIS concepts.

Conventions

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: use [% $now %] to insert the current time stamp.

A block of code is set as follows:

( landcover@1 > 0 AND landcover@1 <= 6 ) * 100

+ ( landcover@1 >= 7 AND landcover@1 <= 10 ) * 101

+ ( landcover@1 >= 11 ) * 102

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

def initGui(self):     # create the toolbar icon and menu entry

    icon_path =