Habits changed even before shelter orders

Even before much of the U.S. closed schools and ordered most businesses to shut down, COVID19 was radically altering the behavior of residents in major cities, according to data gathered by Foursquare, a mobile app that tracks millions of people’s movements.

Its study of foot traffic conducted between Feb. 22 and March 13 found that large numbers of residents in New York, the Bay Area, Seattle and Los Angeles stopped going to food retailers, bars, movie theaters, airports and workplaces.

During the 20day period, the number of New Yorkers ambling into bigbox retailers like Costco to stock up on supplies increased by 50% from normal rates, while the increases in Seattle, the Bay Area, and L.A. were closer to 25%.

The jump in pedestrians walking into traditional grocery stores was also up — about 25% more people in New York and L.A. went to these stores compared to average while the other two cities saw 15% jumps.

At the same time, people were doing less boozing in barrooms and avoiding movie theaters. The number walking into a bar fell by 15% in the Bay Area and between 10% and 15% in the other cities. Air travel, too, fell precipitously, with the number of people walking into airports plummeting by 25% in Seattle, the Bay Area and New York, and by about 15% in Los Angeles.

But by far the biggest change tracked during the period was that many people stopped going into work, especially in Seattle and the Bay Area. In those two areas the number dove by 50%, while the decline was between 10% and 15% in the other two cities.

Foursquare says its analysis includes foot traffic patterns from more than 13 million Americans and uses rolling sevenday averages to account for fluctuations by day of the week.

The bottom line: Many urban Americans were changing their behavior before mayors and governors started shutting down schools and mandating that nonessential workers stay home. Foursquare plans to update the study this week.

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @SFjkdineen