Wild About Math! Making Math fun and accessible

8Oct/073

Are U.S. area codes random?

I had never given much thought to how area codes were selected. I always assumed they were random three digit numbers that, once upon a time, always had 0 or 1 as their middle digit. This morning I was browsing The Universal Book of Mathematics: From Abracadabra to Zeno’s Paradoxes and read an interesting article explaining how early area codes were determined. Here are some snippets from that article:

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 such as 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, 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 go 415, Miami 305, and so on. At the other end of the spectrum came places like Hawaii (the last state annexed in 1959) with 808, Puerto Rico with 809, and Newfoundland with 709…

At another time I will review the book - it is a wonderful encyclopedia of mathematical terms and concepts, and it is sprinkled with nice illustrations and puzzles.

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  1. Interesting stuff! I seem to remember that originally, all area codes had either 0 or 1 as their middle digit. I am not sure why this is so. But they started running out, and now any middle digit is possible (except maybe 9?).

  2. Very interesting indeed.

    I was wondering myself , why San Francisco (415) / Toronto (416) have such a close area code while physically two cities are far apart.

    Thanks!

  3. The area code of Lexington ky is 859


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