The NGA moved its national headquarters to the 51,000-worker Fort Belvoir military base in 2011. And with its arrival came contractors, Gordon said.

He figures new private companies have added at least a million feet of office space — several buildings’ worth — since the NGA arrived.

Moreover, Gordon said, he expects the agency to keep growing.

There are costs, he warned. Federal property isn’t on tax rolls, but the children from all those employees still use public schools. And area roadways have clogged some, no question.

But, with an educated workforce and good public schools, Fairfax County has become a coveted location, he said.

That could — eventually — happen in north St. Louis, too, said Sarah Coffin, an associate professor of urban planning at St. Louis University.

The federal government is about to plant its flag, she said. That sends a message to developers.

“While it might not happen overnight, 10 years after it opens, I am sure there will be spinoff development,” she said.

It’s very important, she added, for the city to guide that growth and hold on to its historic feel.