1 dimension + 1 metric
The pyramid visualization offers an inverted view that permits side-by-side comparison of a metric distributed over two dimensions.
A simple example
Try it with your own data on the Visualization Playground
Let's analyze a bit
In this example we can use the visualization to help us segment our visitors by age and gender. We work with age as the vertical dimension and customers as the metric, then divided into male and female segments.
As our eyes travel down the page, the longest bars stand out which reveal that the majority of our customers are male from age 18-24. Inversely the least-represented demographic in terms of customers is females ages 55-64.