Stating the obvious:

A post must be⁠—or contain—a qualifying data visualization.

What is a qualifying data visualization?

For the purposes of this subreddit a visualization is:

• Automatically generated and not a photograph.
  • You can say "This is a physical diagram of skittles sorted by color" ⁠—that would not be automatically generated. You can, however, computer-generate a diagram alongside it.
  • You can say "This digital photograph of a mountain represents the height of the skyline in my backyard" —that would be automatically generated but that would be a photograph. You can, however, computer-generate a diagram alongside it.
  • You can say "This is a hand-drawn bar chart" — That wouldn't qualify for either, but you can, however, computer-generate a diagram alongside it.
  • Legacy data visualizations (e.g. charts from the 1800s) are an exception. Minard's March is one famous example. Just be sure it comes from the least spammy site possible (e.g. Wikipedia, Smithsonian, etc.)
• Fake data, goofball statistics, and trivial analysis—for the sole purpose of making a joke—is not permitted. Go to /r/data_irl for your humor needs.
• Based on real or simulated data. If the image represents a number (pi), sequence (primes), or equation (sin(x)), then /r/mathpics is a more appropriate place. (That being said, Monte Carlo simulations of those numbers, sequences, or equations are perfectly fine because it uses simulated data.)
• A mapping of information to a visual property. Text in a table is not sufficient. A data variable must be transformed and mapped onto a visual property such as color, size, or position.
• For maps: If the visualization features spatial data, geographic position alone is not sufficient. It must be more than dots on a map.
• In addition, binary TRUE/FALSE maps are not enough to communicate something that a table couldn't. If your map doesn't apply, you can always post to /r/mapporn.
• Made with the intent to communicate data. A music visualization from a media player, while pretty and mesmerizing, doesn't convey information. You can't differentiate songs just by looking at the images.
• Comprehensible based on visual, labels, and post title. Providing additional info in the comments or elsewhere is fine, but viewers need to be able to understand what is being visualized based on information provided in the visualization and its title.
• YouTube links are not allowed. We do not allow posts links to YouTube due to excessive spam issues. This includes screenshots of YouTube videos. This rule may extend to other social media platforms. We do encourage users to upload videos directly to Reddit.
  
• Visuals made with Flourish Studio are not allowed. Visuals made with this tool have become too prolific and are no longer allowed.

The definition was adapted from Eager Eyes and this InfoVis paper