Shapefiles for the tutorial.

Larger map

The map is pretty easy to put together. First you need to produce your choropleth maps. You can do this with some open source GIS programs like QGIS and uDIG. I used ESRI’s ArcMap and exported two images as jpegs. The key here is that the images need to be the same size. Save one image as before.jpg and the other as after.jpg.

Make a folder that will contain your images, html and javascript.

Using a text editor make the html file. Here is the code:

The first part of this code calls jquery and the plugin. Make sure you put the plugin javascript in your folder. The next sections defines the function. The plugin has some options that you can declare. In the body, we declare two divs. These will hold the images. To make the map bigger or smaller change these divs to match your image sizes. Once you have the html, javascript and images together, place the folder on a server. Here is a zip file of my folder.

EDIT: Apparently this plugin has a “No commercial” creative commons licence.

TEXTBOOK
Geospatial Analysis: A Comprehensive Guide to Principles, Techniques and Software Tools

SOFTWARE
OpenGeoDa
STARS (Space-Time Analysis of Regional Systems)
GeoViz Toolkit
SAGA (System for Automated Geoscientific Analysis)
PASSaGE (Pattern Analysis, Spatial Statistics and Geographic Exegesis)
CrimeStat III
Qgis with ftools, manageR

R
There is a Spatial Cran Task View that will load up all the R Spatial modules. These include:

Classes, reading, writing, handling spatial data
Point pattern analysis
Areal data analysisSpatial regression.

In R (case sensitive) type this code:

install.packages(“ctv”)
library(“ctv”)
install.views(“Spatial”)

Two useful packages are:

SpatStat

Maptools

PYTHON

PySal is a Python library for spatial analysis functions.

The forum is at: http://journalismGIS.com/forum

The cities that have been updated are:

Albuquerque, NM
Contra Costa County, CA
Escondido, CA
Long Beach, CA
Norfolk, VA
New Orleans, LA
San Antonio, TX
St Petersburg, FL
Tucson, AZ
Van Nuys, CA

The images are accessed by selecting 45 degree in the satellite map. Then zoom into the area like you normally would. The image will flip to the oblique view as you zoom in.

This is the Safeway in Tucson where the recent shootings took place. These were constructed in Photoshop with screen grabs.

Oblique

Larger version

Overhead

Here is a quick tutorial to show how easy it is to make this interactive Google choropleth map. Download a zip of the project.

This project has 3 parts.

1. A project folder.
2. A folder for the javascript libraries, called “js.”
3. HTML page.

How it works:

First we call the javascript libraries. The first call is for Google Maps. The examples are using V2…so you will need to grab an API code for this to work on your server. The next call is the Cartographer.js library and the third is the Raphael.js library. Cartographer uses the SVG engine from Raphael.

The next section is the javascript that makes the map work. Basically, Cartographer places pre-encoded polygons on the Google map.

The first part of this code creates the Google map.

Then we declare the variables. CountyNames is a alphabetical list of counties in Arizona. PercentBrewer is the percentage of votes Jan Brewer got in the mid-term election.

Next we loop the number of counties and place the counties and the values on the map.

Finally is the Cartographer declarations. ColorScheme can be customized or use a list of standard colors. This uses “RdBu” and then reverses it. The higher the number, the more Red the polygon will be. The lower the number the more Blue it will be. Read more about the choropleth declarations.

(To change counties: Create an alpha list of your counties. Put a dash “-” for any counties with spaces in them, like La-Paz. Change the “AZ-” to your two digit state code. For example CA for California. )

Now we build the map with some HTML.

Here is the complete code.

Download a complete version of this project. Make sure you change the Google map API. More examples of choropleths using this method are available at the Cartographer website.