Book Image

Mastering QGIS - Second Edition

By : Kurt Menke, GISP, Paolo Corti, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP
Book Image

Mastering QGIS - Second Edition

By: Kurt Menke, GISP, Paolo Corti, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP

Overview of this book

QGIS is an open source solution to GIS. It is widely used by GIS professionals all over the world. It is the leading alternative to the proprietary GIS software. Although QGIS is described as intuitive, it is also by default complex. Knowing which tools to use and how to apply them is essential to producing valuable deliverables on time. Starting with a refresher on the QGIS basics, this book will take you all the way through to creating your first custom QGIS plugin. From the refresher, we will recap how to create, populate, and manage a spatial database. You’ll also walk through styling GIS data, from creating custom symbols and color ramps to using blending modes. In the next section, you will discover how to prepare vector, heat maps, and create live layer effects, labeling, and raster data for processing. You’ll also discover advanced data creation and editing techniques. The last third of the book covers the more technical aspects of QGIS such as using LAStools and GRASS GIS’s integration with the Processing Toolbox, how to automate workflows with batch processing, and how to create graphical models. Finally, you will see how to create and run Python data processing scripts and write your own QGIS plugin with pyqgis. By the end of the book, you will understand how to work with all the aspects of QGIS, and will be ready to use it for any type of GIS work.
Table of Contents (19 chapters)
Mastering QGIS - Second Edition
Credits
Foreword
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Index

Complex spatial and aspatial queries


QGIS provides powerful spatial and aspatial query tools that allow for the easy creation of data subsets. In this section, a series of spatial and aspatial queries will be used to determine which elementary schools are within the Southeast Uplift Neighborhood Coalition (SEUL) and Southwest Neighborhoods Inc. (SWNI) coalitions in Portland, Oregon. This example uses the Neighborhoods_pdx.shp and schools.shp sample data.

First, we will select the SEUL and SWNI coalition neighborhoods from Neighborhoods_pdx.shp. To do this, perform the following steps:

  1. Open the attribute table of Neighborhoods_pdx. Click on the Select features using an expression button () to open the Select by expression window. This window is a subset of the Field calculator window that was explained in the Exploring the field calculator interface section earlier in this chapter. If you are unfamiliar with the interface, review the aforementioned section.
  2. In Function list, expand the Fields...