Book Image

Python Geospatial Development - Third Edition

By : Erik Westra
Book Image

Python Geospatial Development - Third Edition

By: Erik Westra

Overview of this book

Geospatial development links your data to locations on the surface of the Earth. Writing geospatial programs involves tasks such as grouping data by location, storing and analyzing large amounts of spatial information, performing complex geospatial calculations, and drawing colorful interactive maps. In order to do this well, you’ll need appropriate tools and techniques, as well as a thorough understanding of geospatial concepts such as map projections, datums, and coordinate systems. This book provides an overview of the major geospatial concepts, data sources, and toolkits. It starts by showing you how to store and access spatial data using Python, how to perform a range of spatial calculations, and how to store spatial data in a database. Further on, the book teaches you how to build your own slippy map interface within a web application, and finishes with the detailed construction of a geospatial data editor using the GeoDjango framework. By the end of this book, you will be able to confidently use Python to write your own geospatial applications ranging from quick, one-off utilities to sophisticated web-based applications using maps and other geospatial data.
Table of Contents (20 chapters)
Python Geospatial Development Third Edition
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Creating an example map


To better understand how the various parts of Mapnik work together, let's write a simple Python program to generate the map shown at the start of this chapter. This map makes use of the World Borders Dataset, which you downloaded in an earlier chapter; copy the TM_WORLD_BORDERS-0.3 shapefile directory into a convenient place, and create a new Python script in the same place. We'll call this program createExampleMap.py.

We'll start by importing the Mapnik toolkit and defining some constants the program will need:

import mapnik

MIN_LAT  = -35
MAX_LAT  = +35
MIN_LONG = -12
MAX_LONG = +50

MAP_WIDTH  = 700
MAP_HEIGHT = 800

The MIN_LAT, MAX_LAT, MIN_LONG, and MAX_LONG constants define the lat/long coordinates for the portion of the world to display on the map, while the MAP_WIDTH and MAP_HEIGHT constants define the size of the generated map image, measured in pixels. Obviously, you can change these if you want.

We're now ready to define the contents of the map. This map will...