A geoesic dome is an almost spherical structure based on a network of great circles (geodesics) lying approximately on the surface of a sphere. The geodesics intersect to form triangular elements that have local triangular rigidity and yet also distribute the stress across the entire structure. It is the only man-made structure that becomes proportionally stronger as it increases in size. Of all known structures made from linear elements, a geodesic dome has the highest ratio of enclosed volume to weight. Geodesic domes are far stronger as complete units than the individual struts would suggest. It is common for a new dome to reach a "critical mass" during construction, shift slightly, and lift any attached scaffolding from the ground. When completed to form a full sphere, it is known as a geodesic sphere.