Wednesday, April 9, 2008

Google Earth and Charts Tutorial

This isn't really a tutorial in the proper sense of the term, but just a posted example of using a combination of KML, NetworkLink, ASP.NET generic handler (ashx), and Google Charts to create a dynamic symbolized map for Google Earth.

I started by downloading some 2000 census data in census block format, along with SF1 data, from ESRI's free download area. Then I brought it into Manifold selecting just a few census blocks for all of Fort Collins, Colorado, and created their inner centroids. I filtered some of the data that had 0 population from the SF1 table. Clearly, when/if you open this up you will find that I should have weeded a few more points, but on the other hand it shows how quick this runs. My server is pretty slow, and I tested this on a wireless internet connection that didn't have a very strong connection (plus I was streaming both Google Earth and some music). In Manifold, I related the two tables and exported it back out to a shapefile. On export I added two columns for lat and long.

In Visual Web Developer Express I created a generic handler (ashx). Instead of going into each line of code, I'll just summariz(s)e. Below is a link to a zip file where you can download both the KML file and the ASHX file. I used Sharpmap 0.9 to connect to the shapefile and read the table's contents. I just took the percentage of Males and Females (number of males / population, number of females / population) for my working statistic (truly groundbreaking stuff :)). You can see from the code that it basically just writes out the KML file, creating a Google Chart api url as it goes.

You can view the final product by opening this KML file in Google Earth. This KML file contains very little KML, and basically just has a Networklink back to the address of the handler.

If you want the files used, they are available here.

As always, any suggestions, comments, questions are much appreciated.

Here are some other examples I've found:

Just noticed the Thematic Mapping Blog also has a post on using charts in Google Earth. Here is the link:
or with open layers


Anonymous said...

Saw your blog on Chart API and Google Earth. Have you noticed that the image doesn't show in the description window now in GE 4.3?

David S. Lamb said...

I posted some more information on this. Seems to only happen when I leave the chart labels turned on...