In an earlier post, I wrote "I agree with Bjørn that the lack of an API-generated legend is problematic, though one could be constructed via HTML adjacent to the chart." However, it turns out that creating a legend is a bit more difficult than I initially thought. The difficulty was brought to my attention via a post to the Google Charts API Google Group that requested help in writing a PHP function to determine the hex value of interpolated colors. Since I figured this would be a common problem, I wrote a PHP 4 class that will hopefully solve it. You can see the tmMapLegend class in action below with the map produced in the earlier tutorial. Learn more about the class and download it here: http://themechanism.com/barkode/code/tmmaplegend/.

•   States carried by the Republicans in all four elections
•   States carried by the Democrats in all four elections
•   States carried by the Republicans in three of the four elections
•   States carried by the Democrats in three of the four elections
•   States carried by each party twice in the four elections

Jeffrey Barke is senior developer and information architect at theMechanism, a maxi-media firm in New York City and London.