According to the The Illustrated Encyclopedia of Hinduism (James G. Lochtefeld, Ph.D.) Hindu and Buddhist texts say that the chakras are arranged in a column along the spinal cord, from its base to the top of the head, connected by vertical channels. Old Buddhist and Hindu texts talk about 4 energy centres and then later 5, 7 and up to 88 000. There is more information on Wikipedia, Britannica, Chopra.com and around the web.
From head to toe 1 circle, divide it in half to get 2 circles (3 overlapping circles), the next scale down uses 4 circles (7 or 9 overlapping circles), the next scale down uses 8 circles (15 or 17 overlapping circles). These circles form 9 energy centres or chakras if you map it from the root to crown.