Book Image

Mastering Geospatial Development with QGIS 3.x - Third Edition

By : Shammunul Islam, Simon Miles, Kurt Menke, GISP, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP
Book Image

Mastering Geospatial Development with QGIS 3.x - Third Edition

By: Shammunul Islam, Simon Miles, Kurt Menke, GISP, Richard Smith Jr., GISP, Luigi Pirelli, John Van Hoesen, GISP

Overview of this book

QGIS is an open source solution to GIS and widely used by GIS professionals all over the world. It is the leading alternative to 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 and getting you acquainted with the latest QGIS 3.6 updates, this book will take you all the way through to teaching you how to create a spatial database and a GeoPackage. Next, you will learn how to style raster and vector data by choosing and managing different colors. The book will then focus on processing raster and vector data. You will be then taught advanced applications, such as creating and editing vector data. Along with that, you will also learn about the newly updated Processing Toolbox, which will help you develop the advanced data visualizations. The book will then explain to you the graphic modeler, how to create QGIS plugins with PyQGIS, and how to integrate Python analysis scripts with QGIS. By the end of the book, you will understand how to work with all aspects of QGIS and will be ready to use it for any type of GIS work.
Table of Contents (18 chapters)
Title Page
Copyright and Credits
About Packt
Contributors
Preface
Index

How to load layers


Loading layers in QGIS involves two 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 for the QGIS framework to be aware of the layer.

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