Lankao is a low-risk area, it will not change color, and the travel code will change color. Travel code is the code of communication big data travel card, which is also equivalent to health code. China Institute of Information and Communication, together with China Telecom, China Mobile and China Unicom, used mobile phones to receive data, which was obtained through the location of the base station where the users' mobile phones were located, providing free inquiry service for mobile phone users nationwide. Mobile phone users can query all the city information they have visited in the previous 14 days through this service.