A large number of namespaces are used to describe the countries, cities, and regions of the world. In fact there are probably too many.
At Factual, we have a lot of geospatial data that we want to send to a browser. It’s often possible to use polygons or images to transmit this data efficiently, but a couple of weeks ago we ran into a case where we needed a floating-point quantity for each map tile pixel. We started by sending the data to the client as JSON, but soon we found that the browser was CPU-bound and spending almost half of the time in the native JSON decoder.