Before revision:  By analysing millions of anonymous mobile phone users' visit trajectories to various places  , the daily and weekly dynamic origin-to-destination (O-D) population flows are computed, aggregated, and inferred at three geographic scales: census tract, county, and state.
After revision:  By analysing millions of anonymous mobile phone users' visit trajectories to various places provided by SafeGraph , the daily and weekly dynamic origin-to-destination (O-D) population flows are computed, aggregated, and inferred at three geographic scales: census tract, county, and state.