Worlds of David Darling
Encyclopedia of Science
   
Home > Encyclopedia of Science

area codes




North American telephone area codes seem to have been chosen at random. But there was a method to their selection. In the mid-1950s when direct dialing of long-distance calls first became possible, it made sense to assign area codes that took the shortest time to dial to the larger cities. Almost all calls were from rotary dials. Area codes like 212, 213, 312, and 313 took very little time for the dial to return to its starting position compared, for example, to numbers such as 809, 908, or 709. The quickest-to-dial area codes were assigned to the places expected to receive the most direct dialed calls. New York City got 212, Chicago 312, Los Angeles 213, and Washington, D.C. 202, which is a little longer to dial than 212, but much shorter than others. In order of decreasing size and estimated amount of telephone traffic, the numbers grew larger: San Francisco got 415, Miami 305, and so on. At the other end of the spectrum came places like Hawaii (the latest state to join the U.S. in 1959) with 808, Puerto Rico with 809, Newfoundland with 709, etc. The original plan (still in use until about 1993) was that area codes had a certain construction to the numbers: the first digit is 2 through 9, the second digit is 0 or 1, and the third digit is 1 through 9. Three digit numbers with two zeros are special codes, i.e. 700, 800 or 900. Three digit numbers with two ones are for special local codes, i.e., 411 for local directory assistance, 611 for repairs, etc.


Related category

   • TYPES OF NUMBER