From the webpage:
D3 allows you to bind arbitrary data to a Document Object Model (DOM), and then apply data-driven transformations to the document. As a trivial example, you can use D3 to generate a basic HTML table from an array of numbers. Or, use the same data to create an interactive SVG bar chart with smooth transitions and interaction.
D3 is not a traditional visualization framework. Rather than provide a monolithic system with all the features anyone may ever need, D3 solves only the crux of the problem: efficient manipulation of documents based on data. This gives D3 extraordinary flexibility, exposing the full capabilities of underlying technologies such as CSS3, HTML5 and SVG. It avoids learning a new intermediate proprietary representation. With minimal overhead, D3 is extremely fast, supporting large datasets and dynamic behaviors for interaction and animation. And, for those common needs, D3’s functional style allows code reuse through a diverse collection of optional modules.
Any description of the graphics on my part would be inadequate. Visit the site, you will see what I mean.
Pay special attention to the architecture of D3, there may be lessons for future topic maps development.
D3 replaces Protovis, which is no longer under active development. Protovis is, however, still suggested as a source of examples, etc.