i use a central database for a few sites all on the same server, they draw the relevant information in from a "zone" i have created in the MYSQL for each site. each url has about a dozen files in it + css.
i'm currently updating ( scrapping and redoing ) them so if you promise to not slag me off here are the the example links so you can see what it produces.
http://www.baybrides.com.au/directory/category/10/Photographers
http://www.tropicalbrides.com.au/cairns/category/10/Photographers
http://www.tropicalbrides.com.au/townsville/category/10/Photographers
http://www.sunshinebrides.com.au/directory/category/10/Photographers
they are all run from my australianbrides admin panel.
i can run as many urls of it as i want.
note: this is olddddd code thus why i'm getting rid of it but i just wanted to detail the potential process you can use.
similar to johno69, IF zone = 17 display X
with this one i can also draw listings from other zones eg: say dubbo = 17 the i can also list NSW and AUST by adding in more zones, then place the client into which ever zone suits them eg: interflora would be AUST, a NSW only vendor would be NSW and thus not show in any zones outside that.
tim