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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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Reprojecting a layer

Layers may be in a CRS other than the one that is best for a given task. Although QGIS supports on-the-fly reprojection when rendering, other tasks, such as performing spatial analysis, may require using a given CRS or having all input layers in the same one. This recipe shows you how to reproject a vector layer.

Getting ready

Open the layer named Davis_DBO_centerline.shp from the sample dataset.

How to do it…

The Davis_DBO_centerline.shp layer uses a CRS with feet as the unit, which makes this unsuitable for certain operations. We plan to use this layer in future recipes to calculate routes and work in metric units, so including this in a CRS that uses them is then a much better option:

Right-click on the layer name in the table of contents and select Save as....
Select Selected CRS in the drop-down list to specify a different output CRS. Click on the Browse button to select a CRS. You will see the CRS selector dialog.
You will be converting the point to the EPSG:26911 CRS. Use the filter box to find it among the list of available CRSs and select it. Then click on OK.
Click on OK in the Save as dialog to create the layer. A new shapefile will be created with the projected lines.

How it works…

Reprojecting is done by the OGR library when it saves the file because this is one of the options that it supports.

There's more…

Raster layers can be reprojected in a similar way:

In the Save as dialog, for raster layers, you can find a CRS field with a Browse button.
Click on it to open the CRS selector, and select the destination CRS.
When you click on OK, the raster layer will be exported using the selected CRS instead of its original one.

Visually different images

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