Welcome to the expanded second edition of Mastering QGIS. The goal of this book is to help intermediate and advanced users of GIS develop a deep understanding of the capabilities of QGIS, while building the technical skills that would facilitate making the shift from a proprietary GIS software package to QGIS. This edition is updated to the latest long-term release version (2.14) and includes descriptions and examples of many new features.
QGIS embodies the open source community's spirit. It seamlessly works with other free and open source geospatial software, such as SAGA, GDAL, GRASS, and LAStools, and supports standards and formats that are published by a myriad of organizations. QGIS is about freedom in the geospatial world: freedom to choose your operating system, freedom from licensing fees, freedom to customize, freedom to look under the hood, and freedom to contribute to the development of QGIS. As you work through this book, we believe that you will be amazed at how much capability and freedom QGIS provides.
QGIS has rapidly risen from the initial version written by Gary Sherman in 2002 to become a globally used and developed volunteer-led project. In 2009, QGIS version 1.0 was released as an Open Source Geospatial Foundation (OSGeo) project and continues to be rapidly adopted worldwide. The enduring support of the open source community has really delivered QGIS to a point where it is now a top-shelf product that should be in all GIS users' toolboxes, and we want this book to be your tour guide and reference as you learn, use, and contribute to QGIS.
Chapter 1, A Refreshing Look at QGIS, reviews the installation and basic functionality of QGIS, which will be the assumed knowledge for the remainder of the book.
Chapter 2, Creating Spatial Databases, covers how to create and edit spatial databases using QGIS. While QGIS supports many spatial databases, SpatiaLite will be used in this chapter. First, core database concepts will be covered, followed by the creation of a spatial database. Next, importing, exporting, and editing data will be covered. The chapter will conclude with queries and view creation.
Chapter 3, Styling Raster and Vector Data, covers styling raster and vector data for display. First, color selection and color ramp management are covered. Next, single-band and multi-band raster data are styled using custom color ramps and blending modes. Next, complex vector styles and vector layer rendering are covered. Rounding out the chapter is the use of diagrams to display thematic map data.
Chapter 4, Preparing Vector Data for Processing, covers techniques useful for turning raw vector data into a more usable form. The chapter will start with data massaging and modification techniques such as merging, creating indices, checking for geometry errors, and basic geoprocessing tools. Next, advanced field calculations will be covered, followed by complex spatial and aspatial queries. The chapter will end by defining new or editing existing coordinate reference systems.
Chapter 5, Preparing Raster Data for Processing, covers the preparation of raster data for further processing using the GDAL menu tools and the Processing Toolbox algorithms. Specifically, these include reclassification, resampling, rescaling, mosaics, generating pyramids, and interpolation. The chapter will conclude by converting raster to vector.
Chapter 6, Advanced Data Creation and Editing, provides advanced ways to create vector data. As there is a great deal of data in tabular format, this chapter will cover mapping coordinates and addresses from tables. Next, georeferencing of imagery into a target coordinate reference system will be covered. The final portion of the chapter will cover testing topological relationships in vector data and correcting any errors via topological editing.
Chapter 7, Advanced Data Visualization, provides advanced ways to display your analysis results. QGIS has a greatly expanded repertoire of layer styling and display options. In this chapter, you will learn how to use Live Layer Effects, utilize the inverted polygon renderer, create an Atlas in the Print Composer, and use the QGIS2ThreeJS plugin to create a 3D view of your data.
Chapter 8, The Processing Toolbox, begins with an explanation and exploration of the QGIS Processing Toolbox. Various algorithms and tools, available in the toolbox, will be used to complete common spatial analyses and geoprocessing tasks for both raster and vector formats. To illustrate how these processing tools might be applied to real-world questions, two hypothetical scenarios are illustrated by relying heavily on GRASS and SAGA tools.
Chapter 9, Automating Workflows with the Graphical Modeler, covers the purpose and use of the graphical modeler to automate analysis workflows. In the chapter, you will develop an automated tool/model that can be added to the Processing Toolbox.
Chapter 10, Creating QGIS Plugins with PyQGIS and Problem Solving, covers the foundational information required to create a Python plugin for QGIS. Information about the API and PyQGIS help will be covered first, followed by an introduction to the iface and QGis classes. Next, the steps required to create and structure a plugin will be covered. The chapter will wrap up after providing you with information on creating graphical user interfaces and setting up debugging environments to debug code easily.
Chapter 11, PyQGIS Scripting, provides topics for integrating Python analysis scripts with QGIS outside of the Processing Toolbox. Layer loading and management are first covered, followed by an exploration of the vector data structure. Next, the programmatic launching of other tools and external programs are covered. Lastly, the QGIS map canvas is covered with respect to how a script can interact with the map canvas and layers within.
To get the most from this book, it is recommended that you install QGIS and follow the explanations. If you choose to do so, you will need a reasonably modern computer with access to the Internet to download and install QGIS, read the documentation, and install plugins. QGIS can run on Windows, Mac OS X, and many Linux distributions.
This book is for intermediate to advanced GIS users, developers, and consultants who are familiar with QGIS but want to look deeper into the software to unleash its full potential. The reader is expected to be comfortable with common GIS functions and concepts, as possession of this knowledge is assumed throughout the book. This book focuses on how to use QGIS and its functions beyond the basics.
In this book, you will find a number of styles of text 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, and user input are shown as follows: "Either of these methods requires the use of the command line, sudo rights, and the apt-get package manager."
A block of code is set as follows:
deb http://qgis.org/debian trusty main deb-src http://qgis.org.debian trusty main
Any command-line input or output is written as follows:
sudo apt-get update sudo apt-get install qgis python-qgis
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "The QGIS interface is divided into four interface types: Menu Bar, Toolbars, Panel, and Map Display."
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