How to relate diferents sub-sites with main site

Hi I would like to create a site with diferent subsite of cities. The main site willl have all the articles and each subsite or city will have its specific content. Something similar that eater.com, it has a main site eater.com and subsites like http://seattle.eater.com/.

I am thinking to create a multisite with wordpress and each subsite will be a city but I am no sure how I can relate all the content to appear in main site and subsite.

Any ideas?

Many thanks.