Most music charts use a variety of fan and consumer data to determine what songs rank in the top 10 for each category. Billboard uses social media interaction and results from research firms to determine its ranking, while iTunes uses an undisclosed formula based partially on purchasing and sales history.
Billboard magazine owns and operates one of the world's largest and most reputable music ranking chart systems. The magazine's first music ranking was released on January 4, 1936, as a hit parade, a term they coined. This list was based on music sales and the amount of airplay songs received on radio stations. In 1940, Billboard began publishing Music Popularity Charts using a slightly more comprehensive method of tabulation. By 1956, these charts were consolidated in the Hot 100 chart.
As of 2015, the Hot 100 calculates ranking based on digital downloads, radio airplay, streaming activity, single sales and several other factors. Each musical genre is distinguished and designated its own chart, and with that some unique points of data. For example, certain genres focus on certain radio stations and music retailers for the data, based on the music's target audience. Each chart has its own manager and staff that monitor the data and update it weekly.