US Mobility trends during the Pandemic

Using cell phone location data, our mobility maps show functional communities over the course of the COVID-19 pandemic in the USA. In Figure 1, the data are grouped by weeks. Each community is marked by a different color. According to these maps, movements of app users are self-organized into multi-scale spatial groups (aka communities). At the top level, we have communities that are close in size to states, but they are not exactly equivalent to the states, rather they often span across several states. In Figure 1, one has the option to show state and county borders, which highlights the differences between states and communities, or counties and communities.

Mega-communities

In Figure 1 you may notice that large communities are combined into mega-communities. Mega-communities are naturally defined travel bubbles, so to speak. The mega-communities are colored with different hues: purple, blue, grey, yellow-brown, pink, and sometimes red. Most commonly, maps in Figure 1 have 5 mega-communities, sometimes 6. Mega-community areas stay more or less constant across all time periods, with some small variations. Some striking variations that we have noticed are 1) Florida and New York belong to the same community at the end of February; 2) in the second week of March, Michigan and New York were in the same community. Such ephemeral community alliances, might explain the spread of COVID during certain time periods. Despite ephemeral inclusions or exclusions, during the majority of the weeks, maps show north-east (purple), south-east (blue), south (pink), mid-west (grey), and the west (yellow-brown). Mega-communities are important because they show how states are interconnected. Knowing these interconnections among communities is important for policy making regarding lifting lockdowns, travel restrictions, etc.

Satellite communities

Some communities have more than one polygon. These are satellite communities. You can find quite a few of those near New York City and New York State. Such communities mean that there are tight connections between them, despite being physically separated by a distance. Satellite communities can be distinguished by color and name.

Small communities

Each large community has a hierarchical structure: they composed of a number of small communities. While maps in Figure 1 show only the outlines of the small communities, Figure 2 allows users to explore small communities that emerged during the week of April 26 - May 2, 2020, which was the end of the lock down in many states.