Local and national in one site

I have been asked to develop a site that has a national front end and then multiple sites within that are localized.

So that if somebody joins on a local site ie Bedford they are contained within that and are not visible or have search functions on say the Glasgow site but would be visible on the national site.

The national site being able to search through all the sub sites. Whereas the local sites are self contained. To join on the national site would direct them to their local site.

I hope somebody can suggest how I can go about developing this as I cant see a way of keeping them seperate yet joined if that makes sense.

A couple examples off the top of my head:

Is this the sort of approach you’re considering?

Is this an existing site you’re modifying, or do you have the opportunity to start from the ground up?

thanks for this - in some ways yes but at each local level I require the viewer to become a member of that region, so they would get a local newsletter, they would be able to search just the local site, and see local content. however when they are on the parent site that would see national content and extracts from the regions. They can join on the main page but it would then direct them to their local region.

There are three levels of joining:

  1. Participants with their own updateable pages.
  2. Viewers who can join in discussions and receive info.
  3. Advertisers - who can place adverts on the site.

It is a totally new site.

I was considering using Joomla but am open to other suggestions.

Whatever I use I can’t figure out how to setup the structure to break it down and keep it both local and national.