For the first exercise we visualized the number 75 and 37 in twenty different ways:
Furthermore we read different articles about the "Gestalt Principles". Those include proximity, similarity, continuation and closure.
Two visual objects close to each other are automatically considered to have a connection. On my visualizations above you can differentiate the two numbers by the gap between the both visualizations.
The same is true for similar visuals.
The next principle continuation is which states that elements arranged on a line or curve are more visually weighted than for example color.
Another principle is closure. Our brain completes images or patterns that are only indicated.
Those principles can be overridden by color:
Source: smashing magazine