[{"gnip":{"matching_rules":[{"value":"bio_location: \"Australia\"","tag":null},{"value":"bio_location: \"Canberra\"","tag":null}],"klout_score":40,"language":{"value":"en"},"profileLocations":[{"objectType":"place","geo":{"type":"point","coordinates":[149.12807,-35.28346]},"address":{"country":"Australia","countryCode":"AU","locality":"Canberra","region":"Australian Capital Territory"},"displayName":"Canberra, Australian Capital Territory, Australia"},{"objectType":"place","geo":{"type":"point","coordinates":[149.12807,-35.28346]},"address":{"country":"Australia","countryCode":"AU","locality":"Melbourne","region":"Australian Capital Territory"},"displayName":"Canberra, Australian Capital Territory, Australia"}]}}]

db.collection.aggregate([{$match:{"gnip.profileLocations.address.countryCode":"AU"}},{$unwind:"$gnip.profileLocations"},{$match:{"gnip.profileLocations.address.countryCode":"AU"}},{$group:{_id:null,results:{$addToSet:"$gnip.profileLocations.address.locality"}}}])