The Location Awareness feature in Vlingo's Options allows for Vlingo to automatically detect where you are located when performing a local search. To enable this feature, open Vlingo's Options and set 'Location Awareness' (under General settings) to On.
Otherwise, if this feature is turned Off, to have Vlingo return results from a particular location, and to avoid having to change your location in the browser each time you search, you can include your location when you speak your search to Vlingo. For example, you might speak "Find ice cream in Boston". This will return the local results you're looking for whether you're using Yahoo! or Google.