Linked from
The 14 pages that link to Similarity (geometry), each with the reason it gives.
TrigonometryRelated: Similar right triangles make side ratios depend only on angle.
GeometryRelated: It distinguishes shared shape from shared size.
Doubling the cubeRelated: Similar cubes scale volume as the cube of their side-length ratio.
ProportionRelated: Similar figures retain the same proportions despite differing in overall size.