BEIJING, Feb. 17 (Xinhua) -- Digital maps have become a key part of China's prevention and control of the novel coronavirus disease (COVID-19) as people gradually return to their cities of residence after an extended holiday.

Local governments are cooperating with mapping service providers to trace the passenger flows in cities and take prevention measures based on the data.

A big data platform developed by Baidu Map updates the population flow data of more than 300 cities every day, including where the passengers come and go, each city's migration scale and trend, as well as urban travel intensity, providing comprehensive information of population flow for the public, media, government and scientific research.

The platform shows that the overall scale of the post-holiday travel rush has dropped significantly compared to previous years.

From the first day of the Lunar New Year to Sunday, the average congestion distance on expressways decreased by 86.6 percent nationwide and the passenger flow in transportation hubs was only 35.6 percent of the same period last year.

However, Xu Yahua, an official with the Ministry of Transport, warned that passenger transport is returning to normal levels as people start returning to work.

The comparison of population flow before and after the holiday shows that there are still a large number of people who have yet to return to their work cities.

The country's biggest cities including Beijing, Shanghai, Guangzhou and Shenzhen will be the hottest destinations for passenger inflow in the following weeks, according to the big data platform.

Local governments can pay close attention to the latest data of population flow on the platform to make sufficient preparations for epidemic prevention and control, said Li Ying, vice president of Baidu and general manager of Baidu Map.

A voice broadcast function to inform drivers of epidemic checks has been launched on the Baidu Map app in a dozen cities.

Traffic police can mark the location of epidemic checkpoints on the platform and app users will hear the voice prompt set by the police when nearing the checkpoints.

Citizens can also use the map app to check whether there were once COVID-19 patients on the vehicles they took or in the places they have been to, in order to confirm whether they are at risk of infection.

Another leading Chinese mapping service provider AutoNavi has opened an online function to the public to detail the passenger flows of the Beijing subway.

Citizens can open the updated AutoNavi app and check whether different subway stations are crowded. The passenger flow density is graded with the colors red, yellow and green.

The subway passenger flow data of the app is provided by the Beijing Municipal Commission of Transport.

Li Meng, a researcher from Tsinghua University, suggested that traffic departments better cooperate with tech firms to provide citizens with the latest public traffic information.

Auto Navi said it is willing to provide the service to more traffic departments of other cities.