The rate of infection is defined as the number of confirmed cases in a combined statistical area (CSA) divided by the total population. A CSA is based on the Unites States Office of Management and Budget classification of US metropolitan and micropolitan areas that are connected economically or socially. Using CSA classifications instead of state data provides a more accurate picture of population centers in the US that would concentrate transmission. Daily case and death numbers are calculated using a simple difference between consecutive days and smoothed using a 7-day moving average. Data are acquired from county level data made publicly available by the New York Times and Johns Hopkins University's Center For Systems Science and Engineering.