NPANXX Detailed Specifications
Detail of Data
Please note: Not every record will have all fields populated
||Two letter USPS state abbreviation
||Area Code (NPA = Numbering Plan Area)
||New Area Code. During the permissive dialling period, the old area code map still
be displayed in the "NPA" field. If blank, then there is no record (yet?) of a split.
If non-blank, then associated NXX is freshly relocated to this new NPA and the NPA in
the "NPA" field (above) would be the old one
||Three digit local number prefix (X=2-9, X=0-9). Generally 201 thru 999.
||Latitude of record for the central office
||Longitude of record for the central office
||Local Access Transport Area
||Popular or political name of city
||Offset from GMT (5=East, 6=Central, 7=Mountain, 8=West, etc..)
||Name of county this record resides in.
||The population of the county from the 2010 Census.
||US ZIP Code or Canadian Postal Code. US codes are five numerical digits, Canadian Postal Codes are 7 character alphanumeric codes.
|ZIP Code Count
||Approximate number of actual ZIP code occurences (listed subscribers) within
0 = Actual count unknown.
|Zip Code Freq.
||Percent frequency of occurrence of this Zip Code in the central office coverage
If > 0, then actual estimated percent, -1 = Most frequent but % unknown, -2 = Second most
frequent, but % unknown.
||Primary use designation. L=Landline, W=Wireless (all wireless; pagers, cellular,
Note that some NXXs may be subdivided between landline and wireless. This is simply
the reported type.
||Version of this product that NXX first appeared. This is not necessarily the NXX
service date, but it should be within 12 months. exception: Since 1994-02-04 was the first version that
included the intro date, then all older NXXs will have an intro date of 1994-02-04 regardless of actual
||1 = NPA recent overlay, blank = Not an overlay
||Ten character Rate Center name for CO. Blank = Rate Center name unknown.
||Eleven character CLLI (Common Language Location Identifier) This field contains
the CLLI code for the central office switch serving this NXX. Blank = Switch CLLI unknown.
||Census Bureau Names for the metro area of the central office.
||Census Bureau ID numbers for the metro area of the central office.
||Census Bureau FIPS code (ID) for the tract of the central office
||1 = Observes DST (Daylight Saving Time) during the normal DST observance period, 0 =
Does not observe DST at all. Some areas of the country such as AZ (except for the Navajo Nation), HI, GU,
PR, VI, and parts of IN do not observe DST.
||Four-character alphanumeric field identifying the NPA-NXX code-holder and/or service provider.
||The name of the phone company the NPA/NXX is registered to.
ZIP Code Information
In addition to the actual ZIP Code itself, there are two data fields that help you to determine how relevant the ZIP Code is. The two data fields are:
ZIP Code frequency of occurence
ZIP Code frequency of occurrence means the percent of all listed subscribers within an NPA/NXX that have a particular ZIP Code. ZIP Codes that have a frequency of occurrence of less than 2% are omitted from the data. That's because those ZIP Codes are statistically insignificant and are quite likely better represented in an adjacent NPA/NXX.
While ZIP Code boundaries rarely change and CO boundaries essentially never change, there is little deliberate alignment of those boundaries. Consequently, there's nearly always overlap of ZIP Code between adjacent COs (NPA/NXX). By evaluating the frequency of occurrence, you can determine a ZIP Code's relevance within an NPA/NXX relative of it's occurrence in an adjacent NPA/NXX.
ZIP Code count
ZIP Code count means the approximate number of actual subscribers within an NPA/NXX that have a ZIP Code listed in the same record. Used with the frequency of occurrence value, the ZIP Code count can help you determine the ZIP Code relevancy.
ex. If a ZIP Code has a high frequency of occurrence, but a very low count, that indicates a NPA/NXX with few listed (or reported) subscriber records.
When using the data to match ZIP Codes to NPA/NXXs, you'll want to consider both a reasonable frequency of occurrence and actual ZIP Code count to help you determine the accuracy of the match. Selecting reasonable frequency of occurrence and ZIP Code count values are up to you depending on your application, but the higher the value the more accurate the match.
ZIP Code Sourcing
Some NXXs have detailed ZIP Code data (Level 2, detailed) where detailed data were available. Other NXXs may only show one or two ZIP Codes without a frequency of occurrence (Level 1, not as detailed). Here is the key to values in the frequency of occurrence field.
If the frequency of occurrence is -1 or -2, then the ZIP Code count for this record is meaningless -- ignore it.
||where nnn is a positive number between 1 and 100. This is the estimated frequency of occurrence for this ZIP Code.
||Most frequently occurring ZIP Code, although percentage is unknown.
||Second most frequently occurring ZIP Code, although percentage is unknown.