How do they come up with the numbers for different area codes?

It seems so arbitrary. I mean it's not like the Simpsons where it's 636 and then 939!!!How do they come up with the numbers for different area codes?
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http://www.nanpa.com/index.htmlHow do they come up with the numbers for different area codes?
There is a lot of history behind how area codes were assigned, driven both by convenience of dialing (higher digits took longer to dial on rotary phones) and the limits of early electro-mechanical routing switches. In the old days area codes always had a 1 or 0 as the middle digit, and never had 1's or 0's as the first digit.



The linked document explains quite a bit more about how area codes are assigned.



As an aside, the North American Numbering Plan (NANP) actually covers 19 countries, allowing to call many different countries with just a 10 digit phone nuber.



In the following "N" represents any digit from 2 to 9 and "X" is any number from 0 to 9.



"This plan carried over the N0X format for single area code states, and N1X format codes for multi-area code states. There were initially 86 area codes assigned (as in the previous 1946 proposal). But Canada was now treated as multi-province, where the provinces followed the same rules as the states in the US. Ontario and Quebec had (as of Oct. 1947) two area codes each, and were assigned N1X codes. The other provinces were assigned one area code each, and had N0X codes. The Maritime Provinces shared a single N0X code (902). This still "exists" to this day in the smaller form that Nova Scotia *AND* Prince Edward Island both share 902."How do they come up with the numbers for different area codes?
Just to expand upon what the first answerer had quoted, the original area codes did indeed only have a 0 or a 1 as the middle digit. This was so the equipment could identify the difference between an in area code long distance call and a long distance call to another area code. Since when making both you dial "1" this was the only way the system could distinguish which type of call you were making.



The smaller numbers are indeed easier/quicker to dial on a rotary phone, with the exception of 0 as it is equivalent to 10 pulses. This, combined with a study showing which digits were easiest for people to remember grouped the prospective codes into a list. It was determined 212 was the easiest to remember and the quickest/easiest to dial, so this area code went to the most populated place in the country, New York City. Next on the list was 313, so it went to the second most populated place, Los Angeles. You get all the way down to Alaska and they're 907 which takes a significantly longer time to dial than 212 and is harder to remember.



The advent of 10 digit dialing and computerized CO equipment allowed for digits other than 0 and 1 be used as the middle digit and allowed for further area code expansions, fueled by pagers first, then second lines for dial up modems and mobile phones.