The Norwood system of classification, published in 1975 by Dr. O’tar Norwood, is the most widely used classification for hair loss in men. It defines two major patterns and several less common types. In the regular Norwood pattern, two areas of hair loss gradually enlarge to produce recession at the temples and thinning in the crown.
https://www.bernsteinmedical.com/hair-loss/men/classification/

