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QGIS 2 Cookbook

By : Mandel, Olaya Ferrero, Anita Graser

5 (1)

QGIS 2 Cookbook

5 (1)

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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

1. Data Input and Output

1. Data Input and Output

Introduction

Finding geospatial data on your computer

Describing data sources

Importing data from text files

Importing KML/KMZ files

Importing DXF/DWG files

Opening a NetCDF file

Saving a vector layer

Saving a raster layer

Reprojecting a layer

Batch format conversion

Batch reprojection

Loading vector layers into SpatiaLite

Loading vector layers into PostGIS

2. Data Management

2. Data Management

Introduction

Joining layer data

Cleaning up the attribute table

Configuring relations

Joining tables in databases

Creating views in SpatiaLite

Creating views in PostGIS

Creating spatial indexes

Georeferencing rasters

Georeferencing vector layers

Creating raster overviews (pyramids)

Building virtual rasters (catalogs)

3. Common Data Preprocessing Steps

3. Common Data Preprocessing Steps

Introduction

Converting points to lines to polygons and back – QGIS

Converting points to lines to polygons and back – SpatiaLite

Converting points to lines to polygons and back – PostGIS

Cropping rasters

Clipping vectors

Extracting vectors

Converting rasters to vectors

Converting vectors to rasters

Building DateTime strings

Geotagging photos

4. Data Exploration

4. Data Exploration

Introduction

Listing unique values in a column

Exploring numeric value distribution in a column

Exploring spatiotemporal vector data using Time Manager

Creating animations using Time Manager

Designing time-dependent styles

Loading BaseMaps with the QuickMapServices plugin

Loading BaseMaps with the OpenLayers plugin

Viewing geotagged photos

5. Classic Vector Analysis

5. Classic Vector Analysis

Introduction

Selecting optimum sites

Dasymetric mapping

Calculating regional statistics

Estimating density heatmaps

Estimating values based on samples

6. Network Analysis

6. Network Analysis

Introduction

Creating a simple routing network

Calculating the shortest paths using the Road graph plugin

Routing with one-way streets in the Road graph plugin

Calculating the shortest paths with the QGIS network analysis library

Routing point sequences

Automating multiple route computation using batch processing

Matching points to the nearest line

Creating a routing network for pgRouting

Visualizing the pgRouting results in QGIS

Using the pgRoutingLayer plugin for convenience

Getting network data from the OSM

7. Raster Analysis I

7. Raster Analysis I

Introduction

Using the raster calculator

Preparing elevation data

Calculating a slope

Calculating a hillshade layer

Analyzing hydrology

Calculating a topographic index

Automating analysis tasks using the graphical modeler

8. Raster Analysis II

8. Raster Analysis II

Introduction

Calculating NDVI

Handling null values

Setting extents with masks

Sampling a raster layer

Visualizing multispectral layers

Modifying and reclassifying values in raster layers

Performing supervised classification of raster layers

9. QGIS and the Web

9. QGIS and the Web

Introduction

Using web services

Using WFS and WFS-T

Searching CSW

Using WMS and WMS Tiles

Using WCS

Using GDAL

Serving web maps with the QGIS server

Scale-dependent rendering

Hooking up web clients

Managing GeoServer from QGIS

10. Cartography Tips

10. Cartography Tips

Introduction

Using Rule Based Rendering

Handling transparencies

Understanding the feature and layer blending modes

Saving and loading styles

Configuring data-defined labels

Creating custom SVG graphics

Making pretty graticules in any projection

Making useful graticules in printed maps

Creating a map series using Atlas

11. Extending QGIS

11. Extending QGIS

Introduction

Defining custom projections

Working near the dateline

Working offline

Using the QspatiaLite plugin

Adding plugins with Python dependencies

Using the Python console

Writing Processing algorithms

Writing QGIS plugins

Using external tools

12. Up and Coming

12. Up and Coming

Introduction

Preparing LiDAR data

Opening File Geodatabases with the OpenFileGDB driver

Using Geopackages

The PostGIS Topology Editor plugin

The Topology Checker plugin

GRASS Topology tools

Hunting for bugs

Reporting bugs

Index

Index

Customer Reviews

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Describing data sources

You can get additional information about a data file before opening it. This recipe shows you how to explore the properties of a data origin.

Getting ready

Before you start working, make sure that you have copied the sample dataset to your filesystem and that you have it located.

How to do it…

In the QGIS browser, navigate to the folder with your sample dataset. Select the elev_lid792_1m file and right-click on it. In the context menu, select Properties. A dialog like the one in the following screenshot will appear:
This dialog displays the properties of a raster layer.
Now, let's select a vector layer instead. Select the elev_lid792_randpts.shp file, right-click on it, and select Properties. The information dialog will look like the following:

How it works…

In the upper part of the description window, you will see a field named Provider. Provider defines the type or data origin and who takes care of reading the data and passing it to QGIS. For raster layers, you will see gdal as Provider. For most file-based vector layers, ogr will be the provider that will appear. They refer to the GDAL and OGR libraries, two open-source libraries that are used by many GIS programs to access both raster and vector data.

There's more…

If the data is already loaded in QGIS, you can access the information about it in the Properties section of the layer (right-click on the layer name to select the Properties entry in the context menu). In the sections displayed in the left-hand side, select the Metadata section. You will see a box containing all the information corresponding to the layer data origin:

There's more…

Functionality provided by the GDAL library, which (mentioned earlier) acts as a provider for raster layers, is also available in the Raster menu. This includes processing and data analysis methods, but it also includes the information tool that is used to describe a raster data source. You will find it by navigating to Raster | Miscellaneous | Info:

There's more…

See also

This is a more complex way to retrieve properties as you can call the tool by adjusting the parameters with more details to get additional information. To know more, check the gdalinfo help page at http://www.gdal.org/gdalinfo.html.

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