My latest is at DataJournalism.com.
It's an essay on the following observation:
The efficiency and multidimensionality of the visual medium arise from a set of conventions and rules, which regularises the communications between producers of data visualisation and its consumers. These conventions and rules are often unspoken: it's the visual equivalent of saying ’it goes without saying’ .
There are lots of little things visualization designers do in their sleep that don't get mentioned. When a visual design deviates from these rules, the readers may get confused.
Here is one example I discussed in the article (hat tip to Xan Gregg).
This pie chart is not easy to read beyond the obvious point that English is the most popular. The following pie chart is much easier on the readers:
The designer follows some common conventions, such as placing the first slice at the top vertical, sorting the slices from largest to smallest (excepting the "other"), and introducing multiple colors only to encode data differences.
These rules are silently applied, and are not announced to the reader. There is a network effect: the more practitioners use these rules, the stronger they stick.
My essay attempts to outline some of the most important unspoken rules of visualizaiton. For more, see here.