For some of the social networks, you will see the option to add a "location" source into your Juicer feed. These locations are based on Google Map IDs, which are strings of letters/numbers that correspond with a geographic location.
In order for Juicer to obtain and display a post from a given location, the poster must tag the location in their post. This happens pretty infrequently, so you might not see many posts pulled into Juicer this way. However, if you are running a campaign, you might request this of your participants.
Keep in mind that you can use Juicer's "Moderate and Filter" panel to further filter the posts obtained for your location source. For example, you could use the "Only allow posts with these words" field to filter the results for a certain hashtag.