Joe (the only name he will give), a homeless man who hangs out in Dupont Circle, in Dupont Circle where his dog was shot by a US Park police officer in Washington, DC. It's been a month since Joe lost his dog, Precious. Since the shooting, there has been an outpouring of concern for Joe and the dog. (Jahi Chikwendiu/The Washington Post)

IF YOU intend to stroll through Dupont Circle, think again. A man may follow you into a Metro car. The homeless may catcall you. Or you may be mugged and shot.

These are the dangers of the historic neighborhood, home to embassies and think tanks, according to SketchFactor, an iPhone application launched this month amid controversy. The app’s co-founders began with a noble vision: Empower communities by crowdsourcing crime and public safety reporting. In a twist on the traditional crime map, regular citizens can rate and comment on the “sketchiness” of their neighborhoods, which will then be displayed as a color-coded pin on a map. The app is “for anyone, anywhere, at any time,” co-founder Allison McGuire said.

That is not how many feel about it. Along with operational problems — such as the fact that comments are not screened before they’re posted — the app has fundamental problems. Chief among those are many ratings that cite the presence of African Americans as a reason for danger. Others involve prejudice against homeless people who pose no safety risk. Just one incident report can have the effect of blacklisting an entire neighborhood.

SketchFactor crowdsources perceptions, not facts — unlike Google, whose famous digital map generates traffic data by processing information from people’s phones. The crowdsourcing of opinions itself is not a misstep. After all, companies that rate hotels or foods, such as or Yelp, collect ratings just like SketchFactor. But this wisdom is revealed only when a critical mass is reached; a Yelp service reviewed by one person, for example, is not as trustworthy as one rated by hundreds. Numbers help guarantee that genuine reviews outrank inaccurate ones.

SketchFactor displays ratings individually without weighing them against other evaluations. It plants each rating like homicide markers on a traditional crime map. That allows ratings to literally color entire neighborhoods. It leads users to develop simplistic views of city blocks based on a few people with iPhone access. Dupont Circle, for example, is among the safest areas in Washington, with seven homicides from 2000 to 2011, but it looks quite risky on SketchFactor’s red-flag-festooned map.

With traditional gatekeepers of information disappearing and more people accessing the Internet, the production of raw data has skyrocketed. Every minute, Google receives more than 2.5 million search requests, more than 40,000 tweets are posted, and 100 hours of video are uploaded to YouTube. Four times as many households have Internet access in 2012 than in 1997. SketchFactor testifies to the promise of this explosion in data, as well as the consequences of not harnessing it correctly.