One of the main rules to follow when advertising is that your ads must target the right market segment of your product. In New York City and Toronto, they are taking this rule to higher levels using gps technology to focus advertisers messages.
When a taxi cab enters New York’s Chinatown, its rooftop sign changes to Chinese. In Toronto, a screen inside the cab will tell passengers when they are near a Starbucks.
Advertisers now can target their audience in a specific city zone or in a well defined “hot spot”. Examples of this uses would be like a financial company would advertise in the downtown zone, while a software company would advertise its product around a convention center using the same cab.
Excerpt from gpsworld.com.