A chart is often used to mean a map or graph of some description, but also the top selling musical hits week by week:
- A map showing coastlines, water depths, or other information of use to navigators.
- An outline map on which specific information, such as scientific data, can be plotted.
- A sheet presenting information in the form of graphs or tables.
- See graph.
- (often charts) A listing of best-selling recorded music or other items: A hit single that reached number 3 on the charts.
All these other definitions have a consistent idea of visual representation of data, but the charts as applied to music is different in that it's a simple one dimensional ranking.
Do they have origins in some particular representation that was more chart-like? Perhaps that got adopted into common usage to create this exception. And possibly related, is there a particular reason it's often charts?