As I currently understand Rackspace CDN, when serving a file, the first users trigger the CDN to put the file being served as close to the users as possible.
However using rackspace cloudfiles, when you create a container, it lets you pick one of 4 regions. What effect does this have on speeds in targeted geos, if any? What is the purpose of the container location if it is just going to move the files to a server near the target geo when traffic starts coming anyway?
The region is for the origin server. Basically you try to upload your content as close as possible so that the caching is more effective. You have to remember unless that file is super busy you're never going to stay in cache, the CDN only works well for very busy content.
https://www.youtube.com/watch?v=XVH7uVHBiE8
Right around 4 minutes starts to talk about your question.
Basically the url you upload to is your Origin server as tyler said.
If abunch of users come from a geographic location rackspace caches the content into "edge servers" in that location. Not sure what the threshold that triggers that copy/cache event, but ya.