https://hiroshinohara.com/2014/05/10/foursquare-%e3%81%ae%e6%96%b0%e3%82%a2%e3%83%97%e3%83%aa-swarm-%e3%81%a7%e3%81%af%e3%83%81%e3%82%a7%e3%83%83%e3%82%af%e3%82%a4%e3%83%b3%e3%81%ae%e6%84%8f%e5%91%b3%e3%81%8c%e5%a4%a7%e3%81%8d%e3%81%8f/