Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By : Joel Lawhead
Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By: Joel Lawhead

Overview of this book

QGIS is a desktop geographic information system that facilitates data viewing, editing, and analysis. Paired with the most efficient scripting language—Python, we can write effective scripts that extend the core functionality of QGIS. Based on version QGIS 2.18, this book will teach you how to write Python code that works with spatial data to automate geoprocessing tasks in QGIS. It will cover topics such as querying and editing vector data and using raster data. You will also learn to create, edit, and optimize a vector layer for faster queries, reproject a vector layer, reduce the number of vertices in a vector layer without losing critical data, and convert a raster to a vector. Following this, you will work through recipes that will help you compose static maps, create heavily customized maps, and add specialized labels and annotations. As well as this, we’ll also share a few tips and tricks based on different aspects of QGIS.
Table of Contents (16 chapters)
QGIS Python Programming Cookbook - Second Edition
About the Author
About the Reviewer
Customer Feedback

Saving a map to a project

Saving a project automatically can be useful for auto save features, or as part of a process to auto-generate projects from dynamically updated data. In this recipe, we'll save a QGIS project to a .qgs project file.

Getting ready

You will need to download the following zipped shapefile and extract it to your qgis_data directory in a subdirectory named ms:

How to do it...

We will create a simple QGIS project by loading a shapefile layer, then we'll access the project object, and save the map project to a file, as follows:

  1. First, we need the Qt core library in the QGIS Python console:

            from PyQt4.QtCore import * 
  2. Next, we load the shapefile and add it to the map:

            lyr = QgsVectorLayer("/qgis_data/ms/mississippi.shp",
                                 "Mississippi", "ogr") 
            reg = QgsMapLayerRegistry.instance() 
  3. Then, we create a file...