This visualization reveals the secrets of animal trading around the world in 2013. It was created by National Geographic and Fathom Information Design, which believe the visualization is useful for researchers and could helping policy makers view animal trade in a different light.
The visualization uses packed circles, which is similar to the classical idiom of Bubble Chart, but the difference is it has interactivity. The data is shown in a hierarchical order, with large animal groups, such as bird and mammals shown initially. When you click on circles, it will drill down to specific species.
The graph only uses one mark and three channels. Each mark presents a specific specie, and surrounded by larger mark which represents a specific group of species. The channel of size encodes the volume of trade and the color is to differentiating the animal species. The channel of hue is applied to represent the purpose of trade. However, one important information, the change rate of trade was not encoded here. I believe that element will show up in its next version, which could provide their audiences with more insights.
Reference:
http://news.nationalgeographic.com/2015/06/150615-data-points-infographic-animal-trade/