Bjørn Sandvik writes the thematicmapping blog, and for the past few days he’s been making a series of posts showing many different ways to use KML to map proportional symbols in Google Earth. The series is well worth reading, and provides plenty of KML examples, so I’m going to post links to each post below with a brief summary. He also has screenshots in the posts. The example here shows population distribution using the Google Chart API where the symbols are sized according to each countries population, and the charts show the distribution according to age. Try it in Google Earth. Here’s a summary of the series of posts:
Making Proportional Symbols in KML – using the placemark icon element to make proportional symbols
Using Google Charts with KML – This innovative KML approach can also be used in Google Maps and Virtual Earth (although the placemark icons don’t scale in those mapping applications).
Drawing Regular Polygons in KML – He points to a PHP application for generating geometric shapes in KML automatically, and then scaling for proportional symbols like circles or squares.
Drawing 3D Bars in KML – I’ve seen this method used the most for these types of maps (see links below).
Proportional Collada 3D Objects in KML – This method could probably be the most fun. Grabbing 3D models from 3D Warehouse and scaling them. He shows an example with a symbolic 3D human for the population graph. Cool!
Here are some previous posts showing some tools and other symbol maps/graphs in Google Earth: