A common design pattern I've used is using a horizontal bar chart to visualize numeric data about a series, and a click through drilldown that discloses a pane with more detailed information about the item that was clicked.
How would you design a similar interaction, but with categorized (two stages) of data? The example below (show a drilldown on domains, and then URL endpoints) is my attempt to both demonstrate the problem and show some potential solutions. The mockups below would show some form of animated transition as a potential user would click from the left most to right most screen... is there a better way? A visualization or interaction pattern I'm not thinking of perhaps?