Because you are out of town low-risk back to turn red code has three aspects:First, inter-provincial or inter-regional activities, leaving the outbreak, high school and low-risk and other key areas, that is, the big data will be generated and pushed to the next destination, the data may be pushed later than the movement of people. Second, the source of data for the health code is mainly the big data pushed by relevant departments and the results of epidemiological investigations, which will be pushed to the next destination only after the outbreak of the epidemic or the delineation of high and medium-low risk zones, so there is a delay in the assignment of the code. Third, at the time of departure, the outbreak has not yet been detected at the place of departure or the medium and high risk zones have not yet been delineated. After the discovery of the epidemic, through the research and judgment, the epidemic may occur the starting time will be projected forward, resulting in the previous period of time to leave the place of personnel as a risk of personnel to be assigned the code