Straightedge and compass construction

way of drawing geometric objects using only an idealized compass and straightedge

Straightedge and compass construction, also known as ruler-and-compass construction, is drawing of lengths, angles or shapes using only a ruler and compass.

Drawing a pentadecagon
Ruler and compass

Some things cannot be drawn this way. For example, there are only 32 regular polygons with an uneven number of sides which are known to be constructible. It has been proven that a square with the same area as the area of a circle cannot be constructed. This is called "Squaring the circle".