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

Understanding map scales


When zooming around the map, we could notice the Scale changing in the status bar. GIS software (apart from web mapping solutions) usually use scales instead of zoom levels. The map scale is an important concept of cartography, and its use was inherited by GIS software. The scale shows the ratio (or representative fraction) between the map and the real world. It is a mapping between two physical units:

For example, a Scale of 1:250,000 means 1 centimeter on the map is 2500 meters (250,000 centimeters) in the real world. However, as the map scale is unitless, it also means 1 inch on the map is 250,000 inches in the real world, and so on. With the scale of the map, we can make explicit statements about its coverage and implicit statements about its accuracy. Large scale maps (for example, with a scale of 1:10,000) cover smaller areas with greater accuracy than medium scale maps (for example, with a scale of 1:500,000), which cover smaller areas with greater accuracy...