Methodology & sources

Two kinds of data

1. Numbering facts (read from NumberResearch). Status, in-service dates, prefix and thousands-block assignment counts, and exhaust forecasts are read directly from NumberResearch.org's public data, which is built on NANPA, CNAC and FCC records. We consume its published data read-only, keep the “as of” date it gives, and link back to it. We never alter its records. If that source is briefly unavailable, we show the last data we retrieved, marked as such, rather than blank the page.

2. Place, relationship and history (compiled by us). Which communities a code covers, whether a change was a split or an overlay, and the dates of each event are compiled by North American Numbers from primary and secondary sources — chiefly the California Public Utilities Commission (CPUC), NANPA, and, as a secondary cross-check, encyclopaedic references. Each page lists the specific sources it used.

How we check it

• We distinguish a split (the map is divided; some numbers change) from an overlay (a second code shares the same ground; no number changes) for every relationship, and verify the type against an authoritative source rather than assuming.
• Where a date or fact rests on a secondary source, or we could not confirm it against a primary record, we say so on the page. We would rather flag a gap than imply certainty we don't have.
• We do not fabricate precise geographic boundaries. Where we don't have authoritative boundary data, we show clearly-labelled schematic relationship diagrams, not a map that looks exact.
• City and community lists are representative of the communities a code serves; we do not claim they are exhaustive or that every listed city is entirely within one code, unless verified against a rate-center record.

What we don't do

• We don't publish “value,” “desirability,” or “most trustworthy” scores for area codes — those aren't properties of an area code.
• We don't generate a page for every possible area-code pair or every city; a public page has to carry real place, relationship or history value.
• We don't identify the current carrier or owner of a number; that requires portability data and is outside an atlas's job.

Dates & updates

Each page shows when its compiled content was last checked, and — for numbering facts — the “as of” date from NumberResearch. We change a page's modified date only when the substance changes, not on every routine deploy. Corrections are handled openly; see Corrections.

AI assistance is used in compiling and drafting; a named editor verifies against sources before publication. See the AI Use Policy.