Similarity (geometry) objects similar if one appears congruent to the other when zoomed in or out at some level. For example, all circles are similar to each other, all squares are similar to each other, and all equilateral triangles are similar to each other. On the other hand, ellipses are not all similar to each other, rectangles are not all similar to each other, and isosceles triangles are not all similar to each other. If two angles of a triangle have measures equal to the measures of two angles of another triangle, then the triangles are similar. Corresponding sides of similar polygons
Euclidean tilings by convex regular polygons figures, which are also called "m"-Archimedean tilings. For edge-to-edge Euclidean tilings, the internal angles of the polygons meeting at a vertex must add to 360 degrees. A regular -gon has internal angle formula_1 degrees. There are seventeen combinations of regular polygons whose internal angles add up to 360 degrees, each being referred to as a "species" of vertex; in four cases there are two distinct cyclic orders of the polygons, yielding twenty-one "types" of vertex. Only eleven of these can occur in a uniform tiling of regular polygons, given in previous sections. In particular, if three polygons meet at a