Image from NYC Bike Share
In mid-20th century urban America, whites emigrated en masse from racially mixed inner-cities to racially homogenous suburbs. According to Malcolm Gladwell, author of The Tipping Point, this white flight from cities occurred abruptly once the African American share of the population in each city reached a critical level, perhaps 20%. Very little white emigration took place while African Americans made up less than 20% of a city's population. However, once the percentage of African Americans reached 20%, massive white emigration occurred suddenly. Gladwell calls situations like these -- where significant change occurs precipitously when a particular condition is met -- tipping points.
Cities attract people with visual impairments for a variety of reasons, for one thing cities are often less auto-dependent than their suburban or rural counterparts. Because they tend to offer more mass transit options, more paratransit options, and friendlier pedestrian environments, cities allow the blind or visually impaired to function independently without having to be driven everywhere. Sadly though, many blind people are unable to partake in one of city life's great pleasures: bicycling. A young non-profit is looking to change that, however. 
