There was no immediate North Korean reaction to Google’s announcement on Tuesday.

Citing privacy concerns, Google would not say how many contributors there were to the new map or who they were, but it said some had used publicly available satellite imagery.

The “citizen cartographers” were able to contribute using Map Maker, a crowdsourcing tool in the style of Wikipedia that allows users to edit or add to Google Maps. The company said the North Korea contributions had been coming in for several years, but Google held back the changes until it had enough to build a credible map and had time to vet the information as best it could, given how closed the North is.

Mr. Melvin, who created the map on the Johns Hopkins site, said he collected data from a variety of sources, including atlases published in North Korea, publicly accessible satellite images and dozens of interviews with defectors, tourists and nonprofit workers who have visited the country.

Google Maps is unlikely to provide important new information to policy makers who already have satellite maps from years of surveillance, nor will it get much of a following in the North itself, where the secretive leaders allow Internet access to only a small portion of the elite, who are closely watched.

But the crowdsourcing project provides a tool for Internet users anywhere in the world to help identify at least some features in the isolated country that the government in Pyongyang does not want the world to know. (The government cherishes secrecy to such an extent that its propagandists liked to boast: “When our enemies try to peek into our republic, they only see a fog.”)

Experts expect some of the more than 24,000 North Korean defectors living in South Korea, one of the world’s most wired countries, to contribute to the map in the future. But their contributions are likely to be limited: most of them come from the northern part of the country, near the border with China, which they cross to escape. Given the tight control on people’s movements in North Korea, most have little knowledge of anything other than their hometowns and the areas nearby.

Already, critics of the North’s authoritarian government and the backward economic policies that keep its people starving were posting sardonic comments by clicking on the “review” link often reserved for rating mapped businesses, restaurants and tourist sites.

One reviewer wrote, regarding bronze statues in Pyongyang of Mr. Kim, the country’s founder, and his son: “Wow, the Korean people must really have loved it under Kim Il Sung, to think they raised this gigantic statue voluntarily on their spare time while they was gloriously lacking food and metal for basic agricultural equipment.”