The Citysense software runs on BlackBerry and iPhone mobile devices and shows a city's busy areas — in this case, San Francisco. (Sense Networks)

It's a slow weekend, and you want to know where the party crowd is — not just among your friends but in the city generally. So, you check your BlackBerry or iPhone, and ta-da, a map of the city shows, in splotches of blue and red, where people are congregating and where taxi cabs are congesting.

A new software application for mobile devices, released this month by a startup U.S. firm called Sense Networks, will do just that. It allows users to see, down to the nearest intersection and in real time, what zones of a city are attracting crowds and what streets have the most traffic.

The brainchild of two U.S. technology professors, Citysense gathers Global Positioning System data from taxis and other GPS-equipped vehicles as well as location information from its users' iPhones and BlackBerrys. It then uses this data to chart how and where people move around and builds up profiles of people's patterns of movement.

By matching the paths of different users, the software can even provide recommendations for a new restaurant, store or nightclub based on the choices of someone with similar tastes.

"We view location — from GPS phones, cars, etc. — as the new hope for understanding people's offline behavior: where are people going, what personality type or 'tribe' they belong to and what to recommend to them," said Tony Jebara, one of the founders of Sense Networks and a computer scientist at Columbia University in New York City.

"We are providing consumers with free applications on their mobile phones for visualizing several cities: Where is everyone? Where should I go eat? Which jazz bar would I like? Where would I like to go shopping? and so on."

Information passed on to advertisers, retailers

Users who load the freely distributed Citysense software on their iPhone or BlackBerry send information about their location to the software's servers, which then combine everyone's details to provide a comprehensive live map of a city's goings-on.

A parallel program, called Macrosense, funnels that information anonymously to third parties, including retailers and advertisers, who want to know where people shop and hang out, or what the best locations for a new billboard would be.

The software can help users visiting a new city, for example, by recommending hot spots, but it also promises to assist businesses in picking the best spot for a new retail outlet, for instance, or better tailoring their marketing.

"Citysense will not only tell you where everyone is right now but where everyone like you is right now," Jebara said. "The application will compare your history and preferences with those of other users and show you where you’re most likely to find people with similar tastes at that moment."

The system, co-developed by Sandy Pentland, a computer scientist at the Massachusetts Institute of Technology, is currently in a test phase in San Francisco and will be rolled out next in Chicago. Subsequent releases are planned for five other U.S. cities.

Citysense is one of a number of the internet's so-called location-based services, also known as LBS or geo sites, that aim to provide detailed, personalized geographic information to users about their surroundings.

Other services include Everyblock.com, which scans news and public records to provide updates on what's happening in a person's neighbourhood; Loopt.com, which maps out for a user where his or her friends are at any given time; and Brightkite.com, which tells you who among your acquaintances have visited different locations around town.

The technology research firm Gartner estimates that the market for such services will reach $8 billion US by 2011, up from $485 million US last year.