During a county fair, the crowd was asked to guess the weight of an ox. None of the guesses was right, but after averaging all of them, the result was nearly exact.
This phenomena is called crowd intelligence or the wisdom of crowds. It sais, a mass of people is more exact in opinions, decisions or guesses, than individuals or even experts.
The Crowd Weather Indicator is based on this theory and represents, how the weather is perceived by the mass. A sunny or rainy day is not the only reason, we sense the weather as positive or negative. Twitter, as an unfiltered database of opinions about everything is the source of the outcome.
A word analyzing algorithm selects messages that are about the weather and categorizes them into positive and negative ones. It also selects only messages within a radius of 25km of the current location of the device. The resulting difference between the good and the bad messages is represented on an abstract scale. The indicator is not showing the actual weather as we know it.
It represent how the crowd feels about it. The result can even be negative on a sunny or positive on a rainy day.
Not the glance out of the window, but the collective decides about the weather.
Weather is just one of many subjects one can use this system on. By changing the algorithm, it is also possible to analyze trends on the stock market or a possible outcome of a sporting event.