The Tropical Songs chart (formerly known as Tropical/Salsa and Latin Tropical Airplay) is a record chart published on Billboard magazine established in 1994. The first number-one song to be published on the chart was "Quien Eres Tu" by Luis Enrique. It features Latin music information from tropical music such as salsa, merengue, bachata, reggaeton, cumbia and vallenato. This chart features only singles or tracks and like most Billboard charts, is based on Airplay; the radio charts are compiled using information tracked by from Nielsen Broadcast Data Systems (BDS), which electronically monitors radio stations in more than 140 markets across the United States. The audience charts cross-reference BDS data with listener information compiled by the Arbitron ratings system to determine the approximate number of audience impressions made for plays in each daypart. The chart was usually posted weekly until the introduction of the Latin Rhythm Airplay Chart in 2005 where it was posted every other week. As of August 2009, the Latin Tropical Airplay is now posted weekly on the Billboard website.