Apple released time series data for countries and cities for each of three modes of getting around: driving, public transit, and walking. The series begins on January 13th and, at the time of writing, continues down to April 20th. The mobility measures for every country or city are indexed to 100 at the beginning of the series, so trends are relative to that baseline. We don’t know anything about the absolute volume of usage of the Maps service.

Source: Apple’s COVID Mobility Data – kieranhealy.org