an Entity references as follows:
Canada Country is a chart published weekly by Billboard magazine. This 50-position chart lists the most popular country music songs, calculated weekly by airplay on 31 country music stations across the country as monitored by Nielsen BDS. Songs are ranked by total plays. As with most other Billboard charts, the Canada Country chart features a rule for when a song enters recurrent rotation. A song is declared recurrent if it has been on the chart longer than 30 weeks and is lower than number 20 in rank. Note that Billboard publishes charts with an issue date approximately 7–10 days in advance.