Book Image

Learning QGIS - Second Edition

By : Anita Graser
Book Image

Learning QGIS - Second Edition

By: Anita Graser

Overview of this book

<p>QGIS is a user friendly open source geographic information system (GIS) that runs on Linux, Unix, Mac OSX, and Windows. The popularity of open source geographic information systems and QGIS in particular has been growing rapidly over the last few years. More and more companies and institutions are adopting QGIS and even switching to it&nbsp;their main GIS.</p> <p>Learning QGIS Second Edition is a practical, hands-on guide updated for QGIS 2.6 that provides you with clear, step-by-step exercises to help you apply your GIS knowledge. Through a number of clear, practical exercises, this book will introduce you to working with QGIS quickly and painlessly. This book takes you from installing and configuring to handling spatial data to creating great maps. You will learn how to load and visualize existing spatial data and create data from scratch. You will perform common geoprocessing and spatial analysis tasks and automate them. We will cover how to achieve great cartographic output and print maps. Finally, you will learn to extend using Python and even create your own plugin.</p>

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Learning QGIS - Second Edition
Anita Graser
Dec, 2014 | 150 pages
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Table of Contents (13 chapters)
Learning QGIS Second Edition
Learning QGIS Second Edition
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
Getting Started with QGIS
Getting Started with QGIS
Installing QGIS
Running QGIS for the first time
Introducing the QGIS user interface
Summary
2
Viewing Spatial Data
Viewing Spatial Data
Loading vector data from files
Dealing with coordinate reference systems
Loading raster files
Loading data from databases
Loading data from OGC Web Services
Styling raster layers
Styling vector layers
Loading background maps
Summary
3
Data Creation and Editing
Data Creation and Editing
Creating new vector layers
Working with feature selection tools
Editing vector geometries
Using the measuring tools
Editing attributes
Reprojecting and converting vector and raster data
Joining tabular data
Summary
4
Spatial Analysis
Spatial Analysis
Clipping rasters
Analyzing elevation / terrain data
Raster calculator
Converting between rasters and vectors
Accessing the raster and vector layer statistics
Creating a heatmap from points
Vector geoprocessing using Processing
Automated geoprocessing with the graphical modeler
Leveraging the power of spatial databases
Summary
5
Creating Great Maps
Creating Great Maps
Advanced vector styling
Labeling
Designing print maps
Summary
6
Extending QGIS with Python
Extending QGIS with Python
Getting to know the Python console
Creating custom geoprocessing scripts using Python
Developing your first plugin
Summary
Index
Index

Creating custom geoprocessing scripts using Python

In Chapter 4, Spatial Analysis, we already used the existing tools in the Processing toolbox to analyze our data, but we are not limited to these tools. We can expand processing with our own scripts. The advantages of processing scripts over normal Python scripts, like the ones we saw in the previous section, are:

  • Processing automatically generates a graphical user interface for the script to configure the script's parameters

  • Processing scripts can be used in the Graphical modeler to create geoprocessing models

A good resource to learn how to write custom scripts for processing is to have a look at the existing scripts in the Scripts section in the Processing Toolbox. As the following screenshot shows, you can access the source code of all the existing scripts through the context menu entry Edit script:

Writing our first processing script

We will create our first simple script that fetches some layer information. To get started, double-click...

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