Editing Overlay complex (section)

==Types==
The [[North American Numbering Plan Administrator]] recognizes several types of overlays:

In a ''distributed overlay'', or ''all-services overlay'', an entire existing numbering plan area (NPA) gains another area code serving the entire area. Most area code overlays are of this kind.

In a ''single concentrated overlay'', only the high-growth portion of an existing area gains a second area code. This was previously implemented in several numbering plan areas, but all of them have since covered entire NPAs.

In a ''multiple concentrated overlay'', the entire existing numbering plan area gains multiple additional area codes, each of which serves a different subsection of the original. This has never been implemented.

In a ''multiple-area distributed overlay'', two or more numbering plan areas gain a single new area code covering the entire area, either concurrently or in phases. Examples include [[area code 872|872]] in [[Chicago]], [[Illinois]] (over [[area code 312|312]] and [[area code 773|773]]) as well as [[area code 587|587]] and [[area code 825|825]] in [[Alberta]] (over [[area code 403|403]] and [[area code 780|780]]). In a phased example, [[area code 564]] was implemented initially only on [[area code 360]] in 2017, but will expand to three other codes when needed, in western [[Washington (state)|Washington]].

A ''boundary-extension overlay'' is a type in which one or more neighboring numbering plan areas (with an overlay code or a primary area code) is expanded. Examples include [[Area code 321|321]] over [[Area code 407|407]] in central [[Florida]] and [[Area codes 778, 236, and 672|778]] over [[Area code 250|250]] in [[British Columbia]]. In 1999, [[Area code 281|281]] was the first of this type, merging with 713 in [[Houston]]. Later that year, [[area code 972|972]] merged with 214, followed by [[Area code 323|323]] merging with 213 in [[Los Angeles]] in 2017, and [[Area code 858|858]], in San Diego, with 619 a year later. In 2023, the first multiple boundary-extension overlay was implemented with the folding of area codes [[area code 602|602]], [[area code 480|480]], and [[area code 623|623]] into a single overlay complex for the [[Phoenix metropolitan area]].

''Service-specific overlays'' are not practiced in the NANP. Only one case, the first overlay area code in the NANPA, [[area code 917|917]], was an example of this. It was established originally as an area code specifically for cellphones and pagers in [[New York City]], but soon afterward, the FCC specified that area codes must not be service-specific, but it grandfathered this use for 917. Later, 917 became available for landline assignments in New York City.