While working at a tedious job in the summer of 1963, Jerry Gretzinger began drawing a map of an imaginary city. He added to the map fitfully for 20 years, put it aside, and then took it up again when his grandson found it in his attic. He’s now been mapping the area around “Ukrania” for more than 30 years, working an average of 20 minutes a day.

The activity is not entirely in his own hands. He draws from a special deck of cards to determine the focus of each day’s work. A given card might tell him to add a new paint color, to shuffle the deck, or to add a new “void,” a region of blankness that obliterates part of the map and incubates a new world of its own. The Ukranians can fend off the void only with a retaining wall, which they are constantly constructing. But whether they can save themselves from oblivion not even Gretzinger knows. “That’s why I keep going,” he says.

The current map covers about 1,500 square feet, representing an area of 14,400 square miles. Here’s a zoomable version.