Data is the core of creating a data visualization. Almost every visual item created in D3 will need to be bound to a piece of data. This data can come from a number of sources. It can be explicitly coded in the visualization, loaded from an external source, or result from manipulation or calculation from other data.
Most data used to create a D3.js visualization is either obtained from a file or a web service or URL. This data is often in one of many formats such as JSON, XML, CSV (Comma Separated Values), and TSV (Tab Separated Values). We will need to convert the data in these formats into JavaScript objects, and D3.js provides us with convenient functions for doing this.