Similar means to have the same shape but not size. Similar also means two or more figures can have their vertices paired to corresponding angles which must be congruent and corresponding sides which must be in proportion. Notice the similar polygons in the figure. The vertices must be matched up with their corresponding vertices. Polygon GHIJ is similar to polygon KLMN. There is a 3 to 1 ratio between polygon GHIJ and polygon KLMN; this is called the scale factor. A scale factor is a ratio of the lengths of a corresponding figure for similar polygons. We can use this factor to eventually figure out the rest of the corresponding sides, by only knowing one of the side's lengths.