Employees stand outside the new Amazon Go grocery store in Seattle, Washington, U.S., on Tuesday, Dec. 6, 2016. David Ryder | Bloomberg | Getty Images

Amazon is becoming a bigger presence in the world of physical retail, through its ownership of Whole Foods stores, the opening of bookstores, its rapid expansion of Amazon Go cashierless groceries and new 4-star stores for popular items. For investors focused on the company's growing footprint, that all made for a confusing disclosure in Amazon's latest annual report, which showed that total square footage for physical stores dropped last year. According to the filing, Amazon's leased and owned physical stores occupied 20.1 million square feet at the end of 2018, down 6 percent from 21.3 million the previous year.

An Amazon spokesperson said in an emailed statement that the drop is the result of a change in how Amazon is reporting its store space to only take into accounts shops that are open. "In 2018, we updated our methodology for reporting physical stores square footage to include only stores open to customers and exclude stores under development," Amazon said. "In the past year, we've increased our physical retail footprint and the number of locations customers can shop, adding Amazon 4-star, Amazon Go, Whole Foods Market stores and Amazon Books stores." It's a minor change for a company that's now valued at about $800 billion, with a massive portfolio that spans online commerce, cloud computing, home devices and entertainment. When taking into account all of Amazon's office space and fulfillment centers across the globe, the company leases and owns a total of over 288 million square feet of space.

A Whole Foods locaton in downtown Denver. John Leyba | Denver Post | Getty Images