At the time of writing, the world is facing the new coronavirus pandemic, which has been declared one of the most dangerous disasters of the 21st century. All nations and communities have applied many countermeasures to control the spread of the epidemic. In terms of countermeasures, lockdowns and reductions of social activities are meant to flatten the curve of infection. Nevertheless, to date, there has been no evaluation of the effectiveness of these methods. Thus, the present study aims to interpret the change in the population density of Sapporo city in the emergency's period declaration using big data obtained from mobile spatial statistics. The results indicate that, in the time of refraining from traveling, the city's residents have been more likely to stay home and less likely to travel to the center area. This has led to a decrease of up to 90% of the population density in crowded areas. The study's outcomes partly explain the statement of reducing 70%–80% of contact between people in line with the purpose of the emergency declaration. Moreover, these findings establish the primary step for further analysis of estimating the efficiency of policy in controlling the epidemic.

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