Knowing the area code of a phone number can provide a rough idea of where the phone is located. However, the amount of land devoted to an area code varies, so it is impossible to trace the number down to a precise physical location just from the first three digits.
Area codes, when first devised in the 1940s, sometimes were assigned to an entire state. Georgia, for example, used 404. Northern California had 916, Central had 415 and Southern had 213. As time went by, more area codes came into existence to free up phone numbers for use. Sometimes area codes are assigned to a single city especially if it is a large metropolitan area, but there is no guarantee.