Size is a powerful retinal variable that is naturally recognisable as a measure of magnitude.
Smaller or thinner or shorter objects naturally indicate lower importance than larger or thicker or taller objects.
Therefore, size is a natural retinal variable for encoding the variation of continuous interval-ratio variables when using point or line visual implantations. The encoding of data points objects and marker labels can vary in size and the encoding of line objects can vary in width. The encoding of area objects does not vary in size because areas are by definition a size object.
Size for focusing attention