Look for location, tag(s) and category(ies) in an input form

I'm trying to figure out how to do the following for this site I'm trying to build. I have a servic开发者_运维百科e table, a category table, a tag table and a location table. Each product belongs to a location (city) and it can have many categories and many tags. My question is: "When a user tries to find a service with something like 'japanese restaurant cheap San Francisco', how could I know which part is the "location"? I know I could use different boxes, but I'm trying to build it this way, and I wonder how sites like Yelp do it.

Thanks in advance :)