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

Converting between raster and vector data models


QGIS provides tools to convert between raster and vector data models. In this section, we will convert between the two data models using a national land cover dataset of 2006 for the Dallas area in Texas.

Converting from raster to vector

To convert a raster to a vector format, QGIS provides the Polygonize tool. The Polygonize tool converts an input raster file into any supported type of vector file and writes the raster cell values to a field in the vector file. When the raster is polygonized, adjacent cells of the same value are aggregated to a single larger polygon.

To access the Polygonize tool, click on Polygonize (Raster to vector) by navigating to Raster | Conversion. The Polygonize tool is shown in the following screenshot and uses the sample Dallas Land Cover.tif file as input:

To convert a raster to a vector polygon, the following options are available:

  • Input file (raster): Input file to be polygonized.

  • Output file for polygons (shapefile...