- Placenames (countries, cities, regions, point of interests - both official and colloquial)
- Latitude and longitude information including bounding boxes
- Hierarchical information about the places - parents and ancestors, siblings, children, and neighbours
All of this is freely available to you. However, this breadth of data is not that obvious, which is why Gary Gale, director of engineering in Yahoo!'s Geo Technology group, came by my desk the other day and asked me to "build something cool with GeoPlanet data." A few lines of PHP (and a solution using YUI and YQL) later, I am happy to present to you the GeoPlanet Explorer.
Check out the following screencast to see it in action and get some more background information on how it was built:
The source code for the GeoPlanet Explorer is available at GitHub.