Approach for building local/city versions of a national website? I'm looking for ideas and advices on how to adapt a national website to cities depending on whether the user is logged in or not.

As for a news website, the front page for anon users would be a mashup of nodes from all the regions.
But registered users will set their city during the registration process or later by editing their profile and will then have a local adapted version of the website.

Any ideas on how to achieve this are welcome
I'd recommend the Domain Access module(s) as the easiest way to set this up with multiple sub-sites (even with sub-domains) but still having a central site to control content and access:


  The Domain Access project is a suite of modules that provide tools
  for running a group of affiliated sites from one Drupal installation
  and a single shared database. The module allows you to share users,
  content, and configurations across a group of sites


It comes with a dozen or so helper modules and a few stand-alone projects that make it easy to create and manage sophisticated site networks.