WP Adverts & Multisites

I am contemplating setting up a WP multi site for a special interest user group that operates from different geographical locations, together with a classified section for each geographical location.
I want to set up each geographical site as a separate sub directory site under the multi site set up. Rather than set up the classified section within each site I want to create just one Classified site, under the multi site set up.
I hope you are with me so far!!
On each geographical site I want to have a link to the one Classifieds site, which will list the ads, for that specific geographical location only. So if a user in Hong Kong is viewing the Hong Kong pages, and clicks the link to the Classifieds section, only the ads for items in the Hong Kong location will show up, and not the ads in London or Sydney.
Is this possible, without having to go to the Classifieds section and then select and sort on location?
Can you offer any other useful advice for my endeavor?
Many thanks!
Chris