Similarity
Similarity occurs when objects look similar to one another. People often perceive them as a group or pattern.

The example above (containing 11 distinct objects) appears as as single unit because all of the shapes have similarity.
Unity occurs because the triangular shapes at the bottom of the eagle symbol look similar to the shapes that form the sunburst.
When similarity occurs, an object can be emphasised if it is dissimilar to the others. This is called anomally.

The figure on the far right becomes a focal point because it is dissimilar to the other shapes.