Fig. 2
From: Universal scaling of human flow remain unchanged during the COVID-19 pandemic
Velocity discretization and The definition of Drainage basins. a, The mean velocity in each square of \(500 \times 500\,\hbox {m}^2\) is calculated by average velocity over those moving people in the square every 30Â min. However, if no one is moving in the square, it is considered missing and not be calculated. b, The average velocity of each square is discretized in 4 directions (north, east, south, west) according to the angle. c, Each square is connected to an adjacent square according to the direction of the arrow. Connected squares are considered to belong to a drainage basin. There are 2 drainage basins in this figure, red and blue, where the color intensity is proportional to the number of upstream squares