We started this chapter by looking briefly at GeoJSON and TopoJSON. If you do anything with maps in D3.js, you will be using one or both of these. We covered it just enough to give an understanding of its structure, and how it is used to define data that can be rendered as a map.

From there, we dove into creating several maps and covered many of the concepts that you will use in their creation. These included loading the data, creating projections, and rendering the geometries within the data.

We examined two projections, Mercator and orthographic, to give an idea of how these present data. Along the way, we also looked at how to style elements on the map, filling geometries with color, and highlighting geometries on mouseover.

Then we examined how to annotate our maps with labels as well as color elements based upon data (choropleths), and to place symbols on the map at specific geographic positions, with a size that is based upon the data.

At this point in the book, we have been pretty thorough in covering much of the core of D3.js, at least enough to make you very dangerous with it. But we have also only ever created stand-alone visualizations, ones that do not interact with other visualizations.

In the next chapter, the final one of this book, we will look at combining multiple D3.js visualizations using AngularJS, and where those visuals also react to the user manipulating other content on their page.