Shortly after the launch of Health Code, under the guidance of China's Ministry of Industry and Information Technology, China ICT Institute, China Telecom, China Mobile and China Unicom jointly launched the itinerary inquiry service. The purpose of run-length encoding is to master the user's travel trajectory more accurately, which can be used as an important evidence to judge whether the user has reached the middle and high risk area, and can prevent the occurrence of omission and hiding.
At first, users can only query by sending short messages, but it didn't take long to upgrade to scanning code query. The key to understanding the user's action trajectory is the mobile phone they carry with them.