Is Belfast the happiest city in Britain? A study used "geo-parsing" technology to analyse patterns in images on the photo-sharing app Instagram. It pinpointed Belfast as having the highest "smile score" based on the average size of the smiles in photos. Bournemouth, Derby, Exeter and Lincoln were also among the top five cities with the highest smile scores, according to the survey by Jetpac, a company that designs "social travel applications... to help people explore the world." London was third from bottom of the study, which included 40 cities, with Salford in last place. Their findings were released to tie in with the launch of the Jetpac City guides, a new iPhone app that curates more than 100 million Instagram photos across more than 5,000 cities. The app aims to help users create their own destination guides using "data imaging" of different places rather than iser reviews and "check-ins" at various destinations. Jetpac says its Instagram-powered travel recommendations "give powerful insights to the authentic feel of a place." Earlier this week, Instagram revealed the most common check-in locations this year, which featured The High Line in New York, the Suvarnabhumi Airport in Bangkok, Dodger Stadium in Los Angeles, New York's Central Park as well as the Staples Center In Los Angeles in the top five. The top 40 happiest cities in Britain, based on smile scores by Jetpac City Guides: Belfast travel guide