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

How to load layers


Loading layers in QGIS involves different steps, which are as follows:

  1. Load the layer. This step creates a variable with the layer information and related data.

  2. Register the layer in QGIS so that it can be used by other QGIS tools.

Loading a layer means loading a reference to the layer and its metadata. The layer is not necessarily loaded in memory, but is usually fetched only when data is accessed to be processed or visualized.

Loading and registering a layer are separate steps. A layer can be loaded, processed, and modified before it is visualized, or it can be loaded as temporary data for an algorithm. In this case, it's not necessary that the QGIS framework would be aware of the layer.

Tip

The iface object has shortcuts to load raster and vector layers in a single step instead of loading and registering them via separate steps.

Every layer type is managed by a provider manager. QGIS has some internal implemented providers, but most of them are external libraries. The list...