Book Image

Practical GIS

Book Image

Practical GIS

Overview of this book

The most commonly used GIS tools automate tasks that were historically done manually—compiling new maps by overlaying one on top of the other or physically cutting maps into pieces representing specific study areas, changing their projection, and getting meaningful results from the various layers by applying mathematical functions and operations. This book is an easy-to-follow guide to use the most matured open source GIS tools for these tasks. We’ll start by setting up the environment for the tools we use in the book. Then you will learn how to work with QGIS in order to generate useful spatial data. You will get to know the basics of queries, data management, and geoprocessing. After that, you will start to practice your knowledge on real-world examples. We will solve various types of geospatial analyses with various methods. We will start with basic GIS problems by imitating the work of an enthusiastic real estate agent, and continue with more advanced, but typical tasks by solving a decision problem. Finally, you will find out how to publish your data (and results) on the web. We will publish our data with QGIS Server and GeoServer, and create a basic web map with the API of the lightweight Leaflet web mapping library.
Table of Contents (22 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Dedication
Preface
14
Appendix

Calculating statistics


In GIS, statistics can be computed from both raster and vector data. However, even calculating raster statistics often involves some kind of vector data. For example, we would like to include some statistical indices in our assessment regarding the suitable areas. More precisely, we would like to include at least the minimum, maximum, and average slope, the minimum, maximum, and average suitability, the average distance from the mass point of the settlements, and the minimum distance from waters. For this task, we cannot use our rasters alone; we need to calculate indices from them only where they overlap with our suitable areas. For this, we need our suitable areas as polygons, and then we can leave the rest of the work to QGIS.

In order to get our suitable areas as polygons, we need to delimit them on our suitability layer. The most trivial first choice is to select every cell with an excellent rating. However, how many cells do we have with more than 75% suitability...