How Visualforce Charting Works

A Visualforce chart is defined using a series of charting components, which are then linked to a data source to be graphed on the chart.
Create a chart with Visualforce by doing the following:
  1. Write an Apex method that queries for, calculates, and wraps your chart data to send to the browser.
  2. Define your chart using the Visualforce charting components.

When the page containing the chart loads, the chart data is bound to a chart component, and the JavaScript that draws the chart is generated. When the JavaScript executes, the chart is drawn in the browser.