Google Maps can’t keep up with Shippensburg. In satellite photos of Exit 24, off Interstate 81 in central Pennsylvania, the 19th century brick and limestone house still stands on White Church Road, as do the silo, bank barn, pole barn, machine shed and the rest of the 102-acre farm. But the next time the satellite passes over, it’ll see what’s also there now: a 1.8-million-square-foot fulfillment center for Walmart Inc. where McKenna Borrell and 500 other people work. Next to the Walmart are four more warehouses and a Sheetz Inc. gas station.

In the past decade, as online shopping has exploded, retailers and consumer goods manufacturers have moved to upgrade their supply chains. They’ve wanted centralized locations to receive and store products that are close to population centers and connected to major transportation networks. The Shippensburg area is that place for much of the Northeast. It’s at most a day’s drive from one-third of the US population and half of Canada’s. It has abundant flat land and a ready labor pool; the toll-free Interstates 81 and 78 lead directly to the Port of New York and New Jersey, the largest on the East Coast. More than 170 million square feet of warehouse space has been built in Pennsylvania along these two interstates since 2014, double the office space in the entire city of San Francisco.