The largest human migration these days takes place every year around this time: Chinese Lunar New Year. Hundreds of millions of humans take every possible avenue to return to their home villages from the cities they now live in. In a space of about one week to 10 days, 3.6 billion passenger miles will be clocked on trains, buses, and cars. The Chinese search engine company Baidu (Google equivalent) created a heat map of these trips gathered from the locations provided by the smartphones of their 200 million subscribers. The three densest nexus you see here are Beijing, Shanghai and Hong Kong/Shenzhen.