#### Overview of this book

Geospatial Analysis is used in almost every field you can think of from medicine, to defense, to farming. This book will guide you gently into this exciting and complex field. It walks you through the building blocks of geospatial analysis and how to apply them to influence decision making using the latest Python software. Learning Geospatial Analysis with Python, 2nd Edition uses the expressive and powerful Python 3 programming language to guide you through geographic information systems, remote sensing, topography, and more, while providing a framework for you to approach geospatial analysis effectively, but on your own terms. We start by giving you a little background on the field, and a survey of the techniques and technology used. We then split the field into its component specialty areas: GIS, remote sensing, elevation data, advanced modeling, and real-time data. This book will teach you everything you need to know about, Geospatial Analysis from using a particular software package or API to using generic algorithms that can be applied. This book focuses on pure Python whenever possible to minimize compiling platform-dependent binaries, so that you don’t become bogged down in just getting ready to do analysis. This book will round out your technical library through handy recipes that will give you a good understanding of a field that supplements many a modern day human endeavors.
Learning Geospatial Analysis with Python Second Edition
Credits
www.PacktPub.com
Preface
Free Chapter
Learning Geospatial Analysis with Python
Geospatial Data
The Geospatial Technology Landscape
Geospatial Python Toolbox
Python and Geographic Information Systems
Python and Remote Sensing
Python and Elevation Data
Real-Time Data
Putting It All Together
Index

## Performing selections

The previous subsetting example is one way to select data. There are many other ways to subset data for further analysis. In this section, we'll examine some of them.

### Point in polygon formula

We briefly discussed the point in polygon formula in Chapter 1, Learning Geospatial Analysis with Python, as a common type of geospatial operation. You'll find that it is one of the most useful formulas out there. The formula is relatively straightforward. The following function performs this check using the Ray Casting method. This method draws a line from the test point all the way through the polygon and counts the number of times it crosses the polygon boundary. If the count is even, the point is outside the polygon. If it is odd, then it's inside. This particular implementation also checks to see if the point is on the edge of the polygon, as shown here:

```def point_in_poly(x,y,poly):
# check if point is a vertex
if (x,y) in poly: return True
# check if point is on...```