A 16TH-century atlas, traceable to Admiral Giovanni Andrea Doria, sold for £1.46 million ($2.6 million) in 2005 at Sotheby’s in London. (Image Courtesy Sotheby’s London.)

"It’s kind of a hunt," Brown says. "The key is to stay in the hunt for a very long time. My approach has been to read and learn and become more and more knowledgeable. This allows me to make my own judgments."

Despite recent price increases, the field remains dominated by passionate collectors, rather than those focused on financial return. Patience is a prerequisite. Commissions can add up to 30 percent to a map’s price, so even maps that appreciate by 10 percent a year require that a collector hold them for at least three years just to break even.

Still, newcomers can acquire attractive, historically significant maps for only a few thousand dollars. Arader recommends spending time getting to know a map librarian, which he did while a student at Yale. The New York Public Library’s Hudson is happy to meet with novices to provide basic training in maps, focusing on features such as paper quality, watermarks and map condition. Maps are best preserved in acid-free liners at controlled temperatures. Those who plan to hang a map should use a museum-quality frame.

Map fans can find information online, in dealer and auction house catalogs and in Map Forum magazine (in print or at www.mapforum.com). Many local map clubs, including the New York Library’s Mercator Society, offer insight. Sotheby’s website features a database of auctioned maps and their prices.

Bidding for an a rare 16th-century Venetian atlas was feverish, despite a recent scandal in the map world.

Hardcore collectors need to develop good relationships with dealers to gain access when the rarest specimens come to market. Collectors say that it helps to specialize; many dealers prefer to sell to a buyer building an important collection on a given subject. "The key is to get the dealer to call you," Brown says.

The walls of Goldstein’s Manhattan apartment are lined with rare maps. One of his favorites is a 1655 depiction of New England and the Dutch colony on Manhattan. After stopping by Arader’s gallery one day with a friend, Goldstein recommended the map to another collector–then returned the following day to buy it himself after the other man passed.

As with McLaughlin’s maps of the fantasy island of California, Goldstein’s map contains more than a few mistakes. The Dutch cartographer, Nicholaes Visscher II, made it to encourage Dutch people to emigrate, so there is a huge section labeled New Netherland–containing towns with English names. "The map is totally messed up," Goldstein admits. But it is also a gorgeous work of art, with original hand-tinted color and gold highlights. He believes his $9,000 investment has easily doubled in value in the five years since he purchased it.

Catherine Curan is a New York—based freelancer.