NATIONWIDE NUMBERING PLAN 855 



two elements, a regional or area code and a central office code. Any 

 outward toll operator, wherever located, will use that same designation 

 in r(>aching that office through the dial toll switching network. 



In a sense, all of the thousands of offices involved are to be treated 

 as though the}' were contained in one huge multi-office cit3^ Toll opera- 

 tors will use the area code and the office code in reaching an office situated 

 outside her own numbering plan area, while on calls to points within 

 her own numbei-ing plan area she will dial only the number as listed for 

 toll in the directory. In principle the method employed is to divide the 

 two countries geographically into numbering plan areas and to give 

 each of these areas a distinctive code. Refer to Fig. 1. Within each of 

 these numbering plan areas each office will have a code unlike that of any 

 other office in the same numbering plan area and also unlike any area 

 code. Hence for toll dialing pui'poses each office will have an area code 

 and central office code which will form a combination unlike that of any 

 other central office in the two countries. 



In this geographical division into numbering plan areas, border lines 

 between states and between Canadian provinces have generally been used 

 as mmibering area boundaries. Since about 500 central offices are the 

 maximum number which can be served in a numbering plan area, it is 

 necessar>^ to divide the larger and more populous states and provinces 

 into two or more areas making, of course, due allowance for growth. 

 Xew York state with the largest number of central offices is divided 

 into six numbering plan areas; Pennsylvania, Illinois, Texas and Cali- 

 fornia have four areas each. Other divided states have three or two areas 

 depending upon the number of offices to be served. Approximately 90 

 areas are being provided, with 14 states and two provinces served by 

 two or more numbering plan areas, the remaining states and provinces 

 by one area each. 



In fixing the intrastate numbering plan area boundaries of subdivided 

 states, among other considerations effort was made to avoid cutting 

 across heavy toll traffic routes in order to have as much of the toll traffic 

 as possible terminating in the area in which it originated. The advantage 

 of arranging the numbering plan areas in this manner is readily apparent 

 since on this traffic which does not pass an area boundary the area code 

 is not required. 



Let us now consider the composition of the area codes. As indicated 

 previously they must be of a type which will enable the switching equip- 

 ment to distinguish them from the codes of central offices. 



On the telephone dial plate letters are assigned only to the dial posi- 

 tions 2 to 9, inclusive (on some dial plates a Z appears on the position 



