It's called a semi-log plot. X is linear time, Y is log population count. The slope of exponential-like acceleration phase indicates the growth rate. PS: this

It's called a semi-log plot. X is linear time, Y is log population count. The slope of exponential-like acceleration phase indicates the growth rate. PS: this type of data is much better modeled by relatively simple ordinary differential equations because the rate of change of a communicable disease is proportional to the number infected.