A map of D.C., by aliens, for aliens.

Ten thousand years in the future, space aliens land in an uninhabited Washington and discover a city dominated by the remnants of neoclassical architecture. With all of D.C.’s columned museums, government buildings and white marble monuments, the aliens (apparently finding no items once contained in the Museum of Natural History) assume that Earth’s civilization was centered here, before it spread all over the world. They see Washington as we see ancient Greece or Rome. They even give us a name: Pillar-Builders.

As the aliens explore more of the planet, they make other mistakes, too. They think, with the Earth covered in so much water, humans must have been aquatic beings. They also “give us the benefit of the doubt,” says Sarah Newman, who curated “Ellen Harvey: The Alien’s Guide to the Ruins of Washington, D.C.,” a thoughtful, often-hilarious interactive exhibit commissioned as part of the Corcoran Gallery of Art’s NOW series of D.C.-centric, site-

specific works. “They think we were very peaceful and that we must have been telepathic to get the buildings to look the same all over the world.”

In essence, the exhibit’s aliens make some of the same mistakes humans have made about our own history. “It’s meant to be a commentary on our very imperfect understandings of past civilizations,” says Harvey, who was born in the U.K. and works in Brooklyn. “People always interpret the past in light of the present.” Here, viewers of the show see our own past and present reflected back, scrambled badly by future visitors.

The exhibit comprises four elements. There’s a large mock-up sculpture of a spaceship inspired by the

Pillar-Builders’ aesthetics (it looks like a Corinthian column turned upside down and features 37 floors of high-end living amenities) and a souvenir stand where alien visitors (but not human museuExhibitsmgoers) can buy paintings of various ruined buildings to remember their trip to Earth. One room, covered with more than 3,000 postcards depicting real-life classical and neoclassical architecture from different periods worldwide, represents the aliens’ attempts to figure us out.

“The other night I had a nightmare that they all fell down,” Newman says, spotting one card threatening to make a break from its double-sided tape and pressing it back to the wall.

The fourth element and the centerpiece of the show is actually portable — and available all over the city. It’s a colossally botched map guiding visitors to some of our greatest landmarks. The Corcoran itself is on there, described as the “Inside-Out Pillar Thing”; the “The Really Complicated Pillar-Thing” (the Capitol) and “The Flat Pillar-Thing” (the Lincoln Memorial) are also among the sights to be seen. You can find the maps at the gallery as well as at hotels and tourist stops all over the city — making D.C. itself the largest part of the exhibit.

“D.C. is a spectacle,” Harvey says. “I thought, ‘Wouldn’t it be interesting for people to come to a show that then takes you back out to D.C. seeing it in a different light?’”

As for Newman, having the most important component of the show be both inside the gallery and out is the most exciting part: People who come across the map unexpectedly will react to an installation they didn’t even realize surrounded them.

“I keep picturing tourists picking up this map and being deeply, deeply confused,” she says. Which, in a way, makes anyone engaging with the artwork aliens themselves.

Corcoran Gallery of Art, 500 17th St. NW; through Oct. 6, $10; 202-639-1700. (Farragut West)