This graph chart shows the subcategories' topology belonging to the main category.
Having just one category (or level) is a bad practice on Wikimedia Commons because makes difficult to the community to find and use files. Instead a multilevel and articulated categorization permits better reuse of the uploaded media.
This statistic is updated every day (max lag time 24h) and represents the actual scenario.

How to read it
Each node represents a category, while the edges are the relations. Categories at the same level share the color.The bubble size is proportional to the amount of files within every category.

How to use it
On the right menu you can order categories by level or by number of files. If you click into a category name the correspondent node will highlight (and vice versa).
On the top bar you can also drill-down to a chosen subdirectory.

Use case
With this graph you can understand if the media files of your interest are divided in a useful way. Probablya category with more then one hundred files needs to be splitted in two or more subcategories. In fact, the better a media is categorized on Wikimedia Commons, the more is probable to be viewed or used inside a Wikipedia page.
More info available on: https://commons.wikimedia.org/wiki/Commons:Categories.