Even though it's easy to create stand alone charts in d3.chart, often you may want to combine your charts into a single chart. Think small mutliples for example, where a single chart type repeats in sequence, rendering different parts of the data.
For a detailed description of how one would go about composing charts together see our github wiki page on Composing Charts.
You can also see an example of a composable chart on our examples page here:
In this example we create a chart that is a combination chart of two other charts: a bar chart and a pie chart.