| Field Name | Data Type | Description |
|---|---|---|
| NPA | Char(3) | Area Code (NPA = Numbering Plan Area) |
| NXX | Char(3) | Three digit local number prefix (X=2-9, X=0-9).Generally 201 thru 999. |
| CountyPop | Integer | Estimated population to nearest 1000. This is a very rough estimate based on 1990 census data! |
| ZipCodeCount | Integer | Approximate population of the ZIP code. |
| ZipCodeFreq | Integer | Percent Frequency of Occurrence of this ZIP Code in the NPANXX area. If = 0, then unknown If = -1, then the ZIP Code is the most frequent, but % unknown If = -2, then the ZIP Code is the second most frequent, but % unknown |
| Latitude | Decimal(12, 8) | Latitude of record for the central office |
| Longitude | Decimal(12, 8) | Longitude of record for the central office |
| State | Char(2) | Two letter USPS state abbreviation |
| City | VarChar(255) | Popular or political name of city |
| County | VarChar(255) | Name of county |
| TimeZone | VarChar(255) | Offset from GMT (5=East, 6=Central, 7=Mountain, 8=West, etc..) |
| ObservesDST | VarChar(255) | 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. |
| NXXUseType | VarChar(255) | Primary use designation. L=Landline, W=Wireless (all wireless; pagers, cellular, PCS, etc.) Note that some NXXs may be subdivided between landline and wireless. This is simply the reported type. |
| NXXIntroVersion | VarChar(255) | Version of this product that NXX first appeared. |
| ZipCode | VarChar(255) | ZIP Code (United States) (five digits) |
| NPANew | VarChar(255) | New Area Code. During the permissive dialing 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 |
| FIPS | VarChar(255) | Census Bureau FIPS code (ID) for the tract of the central office |
| LATA | VarChar(255) | Local Access Transport Area |
| Overlay | VarChar(255) | 1 = NPA recent overlay, blank = Not an overlay |
| RateCenter | VarChar(255) | Ten character Rate Center name for CO. Blank = Rate Center name unknown. |
| SwitchCLLI | VarChar(255) | This field is now blank and will be removed in a future version of the database. The data will no longer be available. |
| MSA_CBSA | VarChar(255) | Census Bureau Names for the metro area of the central office |
| MSA_CBSA_Code | VarChar(255) | Census Bureau ID numbers for the metro area of the central office |
| OCN | VarChar(255) | Four-character alphanumeric field identifying the NPA-NXX code-holder and/or service provider. |
| Company | VarChar(255) | The company name. |
| CoverageAreaName | VarChar(255) | The name of the area this NPA-NXX Covers. This is primarily the city name but other Alias Names may be used. |
| NPANXX | Char(6) | The NPA and NXX combined. |
| Flags | VarChar(35) | Any flags indicating specific things about this data record. |
| Status | VarChar(35) | Indicates if this NPANXX is in active use ("Active" or "Inactive") |
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.
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.
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.
| nnn | where nnn is a positive number between 1 and 100. This is the estimated frequency of occurrence for this ZIP Code. | -1 | Most frequently occurring ZIP Code, although percentage is unknown. |
| -2 | Second most frequently occurring ZIP Code, although percentage is unknown. |