Book Image

QGIS 2 Cookbook

By : Mandel, Olaya Ferrero, Anita Graser
Book Image

QGIS 2 Cookbook

By: Mandel, Olaya Ferrero, Anita Graser

Overview of this book

QGIS is a user-friendly, cross-platform desktop geographic information system used to make maps and analyze spatial data. QGIS allows users to understand, question, interpret, and visualize spatial data in many ways that reveal relationships, patterns, and trends in the form of maps. This book is a collection of simple to advanced techniques that are needed in everyday geospatial work, and shows how to accomplish them with QGIS. You will begin by understanding the different types of data management techniques, as well as how data exploration works. You will then learn how to perform classic vector and raster analysis with QGIS, apart from creating time-based visualizations. Finally, you will learn how to create interactive and visually appealing maps with custom cartography. By the end of this book, you will have all the necessary knowledge to handle spatial data management, exploration, and visualization tasks in QGIS.
Table of Contents (14 chapters)
13
Index

Creating views in SpatiaLite

In a database, view is a stored query. Every time you open it, the query is run and fresh results are generated. To use views as layers in QGIS takes a couple of steps.

Getting ready

For this recipe, you'll need a query that returns results containing a geometry. The example that we'll use is the query from the Joining tables in databases recipe (the previous recipe) where attributes were joined 1:1 between the census polygons and the population CSV. The QSpatiaLite plugin is recommended for this recipe.

How to do it…

The GUI method is described as follows:

  1. Using the QspatiaLite plugin (which is in the Database menu, if you've activated it) place the following in the query:
    SELECT *
    FROM census_wake2000 as a
    JOIN census_wake2000_pop as b
    ON a.stfid = b.stfid;
  2. From the Option dropdown, select the last choice, Create Spatial View & Load in QGIS, and set the Geometry field box value to the name of your geometry field from your spatial layer....