This sample illustrates Facebook users in a chart for different countries over several years. In a line-based series, data points can be annotated using symbols.
Each points in a series can be represented as a symbol through marker. We can also customize the shape, size and color of a symbol through marker properties.
Tooltip is enabled in this example, to see the tooltip in action, hover a point or tap on a point in touch enabled devices.
More information on the marker can be found in this documentation section.