Overlay plan
Encyclopedia
In telephony
, especially in North America, an overlay plan is the practice of introducing a new area code by applying it onto a geographic
area that is already occupied by one or more existing area codes, resulting in two (or more) area codes serving the same area.
; today 206 applies to only the city of Seattle and immediate vicinity. This practice became known as a split plan
.
In a number of cases, overlay plans were implemented on a special case basis to implement specialized dialing plans. In some areas, a party in one area code could dial a prefix which was local, but in a different area code, with only 7 digits. If they were calling a distant prefix in the same area code, they would either have to dial 1+ the number or 1+area code+ the number.
This practice was done on a large scale in the City of Washington, DC and its suburbs in Maryland and Virginia. Until 1991, any telephone in the Washington, DC metropolitan area could dial any local number in the District, Maryland or Virginia by dialing the 7-digit number. The way this was implemented was that every telephone in Maryland and Virginia that was in the Washington Metropolitan area was given a 'hidden' phone number consisting of the same number in the 202 area code, essentially making the 202 area code an overlay over the entire region. This meant a number in Virginia, actually in the 703 area code such as 931-xxxx could have been dialed as 703-931-xxxx or as 202-931-xxxx, while a Maryland number such as 585-xxxx which is actually in the 301 area code could be dialed as 301-585-xxxx or 202-585-xxxx. This also meant no prefix could be duplicated in any of the three jurisdictions. By 1991 the demand for more numbers was too great, the use of area code 202
as an overlay was discontinued, and callers in the area dialing an out-of-area-code number had to dial the full 10 digit number.
accelerated the rate of expansion of metropolitan areas, and multiple split plans have caused the geographical area of a given area code in those regions to shrink. Also, the rapid growth in popularity of mobile phone
s, in addition to regular land line growth, has increased demand for new phone numbers even more.
The rise in popularity of mobile phones has added to the pressure against split plans, as an area code change affecting the exchange in which a cell phone is based requires the wireless carrier to reassign the number of every device based in those areas.
(i.e., the area code must be included), even for local call
s, in the affected area. This and the difficulty of remembering all the area codes in a geographic area made overlay plans only marginally less unpopular than split plans. 10-digit dialing is not a technical requirement but a U.S. Federal Communications Commission
(FCC) mandate to promote fairness among telephone companies.
The first example of an entire state previously only served by a single code being overlaid was in West Virginia.
Overlays have also become more popular than split plans in Canada during the previous decade. All of British Columbia and Alberta, and large parts of Ontario and Quebec are currently overlaid. By 2013, all of Quebec, all of Manitoba and almost all of Ontario will be overlaid as well.
. This has noticeably slowed the need for area code growth, but not completely. For example, the Western Washington
area narrowly avoided needing an overlay in 2001. Area code 564
, originally planned for introduction in October 2001, was canceled in August 2001 after state regulators determined that the existing number pool had begun to be used more efficiently.
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
, especially in North America, an overlay plan is the practice of introducing a new area code by applying it onto a geographic
Geography
Geography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
area that is already occupied by one or more existing area codes, resulting in two (or more) area codes serving the same area.
Methodology
Prior to the introduction of overlay plans, the method of introducing new area codes (also known as numbering plan areas or NPAs) in a region was to divide the existing territory of one area code into two (or more) pieces, allowing the more established or developed section to retain the original area code, and changing the numbering space of the other section(s) to have a new area code. For example, the original area code for the entire state of Washington was 206Area code 206
206 is the North American telephone area code in the U.S. state of Washington for Seattle, the islands of Mercer, Bainbridge and Vashon, and portions of metropolitan Seattle from Des Moines to Woodway....
; today 206 applies to only the city of Seattle and immediate vicinity. This practice became known as a split plan
Split plan
In telephony, a split plan is the practice of introducing a new area code by dividing an existing area code's territory and applying the new area code to one of the resulting divisions, replacing the existing area code within that section....
.
In a number of cases, overlay plans were implemented on a special case basis to implement specialized dialing plans. In some areas, a party in one area code could dial a prefix which was local, but in a different area code, with only 7 digits. If they were calling a distant prefix in the same area code, they would either have to dial 1+ the number or 1+area code+ the number.
This practice was done on a large scale in the City of Washington, DC and its suburbs in Maryland and Virginia. Until 1991, any telephone in the Washington, DC metropolitan area could dial any local number in the District, Maryland or Virginia by dialing the 7-digit number. The way this was implemented was that every telephone in Maryland and Virginia that was in the Washington Metropolitan area was given a 'hidden' phone number consisting of the same number in the 202 area code, essentially making the 202 area code an overlay over the entire region. This meant a number in Virginia, actually in the 703 area code such as 931-xxxx could have been dialed as 703-931-xxxx or as 202-931-xxxx, while a Maryland number such as 585-xxxx which is actually in the 301 area code could be dialed as 301-585-xxxx or 202-585-xxxx. This also meant no prefix could be duplicated in any of the three jurisdictions. By 1991 the demand for more numbers was too great, the use of area code 202
Area code 202
Image:Area code 202.svg|right|The area colored red indicates the geographical region of the District of Columbia, served by area code 202poly 0 50 49 54 103 84 111 88 101 107 118 130 143 139 179 140 211 188 238 203 260 240 259 248 248 250 255 262 253 357 1 357 Area codes 571 and 703poly 1 1 0...
as an overlay was discontinued, and callers in the area dialing an out-of-area-code number had to dial the full 10 digit number.
Rapid growth
Urban sprawlUrban sprawl
Urban sprawl, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburbs to its outskirts to low-density and auto-dependent development on rural land, high segregation of uses Urban sprawl, also known as suburban sprawl, is a...
accelerated the rate of expansion of metropolitan areas, and multiple split plans have caused the geographical area of a given area code in those regions to shrink. Also, the rapid growth in popularity of mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
s, in addition to regular land line growth, has increased demand for new phone numbers even more.
The rise in popularity of mobile phones has added to the pressure against split plans, as an area code change affecting the exchange in which a cell phone is based requires the wireless carrier to reassign the number of every device based in those areas.
Reluctant solution
To alleviate complaints about such changes, in 1992 the telecommunication industry began to introduce "overlay plans" as a means to introduce new area codes. In this model, one fixed geographic area would concurrently have multiple valid area codes throughout. This plan's main benefit, which addressed many of the issues causing resistance to split plans, was that all existing phone numbers remained unaffected by the new area code. Newly-assigned numbers in the overlay plan areas would have the new area code. As a result, two telephones, located next to each other in the same building or house, could have different area codes. New York was the first area to employ this solution, using the 917 area code in addition to the older 212.Compromise
However, overlay plans introduced a new inconvenience: mandatory 10-digit dialing10-digit dialing
In the United States and Canada, 10-digit dialing is a popular term used to refer to the practice of including the area code of a phone number when dialing...
(i.e., the area code must be included), even for local call
Local call
In telephony, the term local call has the following meanings:# Any call using a single switching center; that is, not traveling to another telephone network;# A call made within a local calling area as defined by the local exchange carrier;...
s, in the affected area. This and the difficulty of remembering all the area codes in a geographic area made overlay plans only marginally less unpopular than split plans. 10-digit dialing is not a technical requirement but a U.S. Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) mandate to promote fairness among telephone companies.
Popularity
Overlay plans have been used much more widely in some areas than others. For example, the northern third of Ohio is covered by two large overlay complexes, as is northern Georgia. Connecticut, Illinois, Oregon, New Jersey, Massachusetts, Maryland, and Texas have also used overlays heavily, and are (or soon will be) completely or mostly overlaid. In California, on the other hand, only four of 27 areas have overlays, and all were very recently implemented.The first example of an entire state previously only served by a single code being overlaid was in West Virginia.
Overlays have also become more popular than split plans in Canada during the previous decade. All of British Columbia and Alberta, and large parts of Ontario and Quebec are currently overlaid. By 2013, all of Quebec, all of Manitoba and almost all of Ontario will be overlaid as well.
Types of overlays
The North American Numbering Plan Administration recognizes different forms of overlays:- Distributed overlay (or all-services overlay): an entire existing area gains another area code serving the entire area. Most overlays are of this kind.
- Single concentrated overlay: only the high-growth portion of an existing area gains a second area code.
- Multiple concentrated overlay: the entire existing area gains multiple additional area codes, each of which serves a different subsection of the original. There are no known examples of such being implemented in the NANPA.
- Multiple-area distributed overlay: two or more area codes gain a single new area code covering such an area. Examples include 872Area code 872Template:Cite webArea code 872 is a North American Numbering Plan overlay of area codes 312 and 773 in Chicago, Illinois, and entered service on November 7, 2009.-External links:* at North American Numbering Plan Administration's website*...
in ChicagoChicagoChicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
, IllinoisIllinoisIllinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
(over 312Area code 312Area code 312 is the telephone area code for the Chicago Loop and surrounding areas of the city of Chicago, Illinois. Prior to the split on November 11, 1989, forming 708 , 312 area code originally served much of Greater Chicago...
and 773Area code 773Area code 773 went into effect in the city of Chicago, Illinois, on 12 October 1996. The area code covers the city, excluding the downtown core. Originally, the entire city and suburbs were in area code 312. Then, in 1989, area code 708 was created for the suburbs, leaving a rump 312...
) and 587Area code 587Area code 587 is a telephone area code that covers all of Alberta, Canada, in addition to the incumbent codes, 403 and 780. Numbers in this area code started being allocated in late 2008....
in AlbertaAlbertaAlberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
(over 403Area code 403Area code 403 is a telephone area code in the Canadian province of Alberta, encompassing the southern half of the province, including the Calgary area...
and 780Area code 780Area code 780 is a telephone area code in the province of Alberta, encompassing the northern two-thirds of the province. The code was established in 1999; prior to this date the entire province was served by the 403 area code...
). - Boundary-extension overlay: a neighboring area code (either an overlay code or single primary area code) is expanded to serve the area as well. Examples include 321Area code 321Area code 321 is the area code serving Brevard County, Florida. The area code has been in use since November 1, 1999; it was assigned to the area, instead of suburban Chicago, after a successful petition led by local resident Robert Osband to commemorate the Space Coast's impact on the county. The...
over 407Area code 407Area code 407 is the area code for the Orlando metro area including all of Orange, Osceola, and Seminole counties, as well as small portions of Volusia and Lake counties. From 1947 until 1988, the 407 area code was part of the 305 area code, which included the east coast from Brevard County...
in central FloridaFloridaFlorida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
and 778Area code 778Area code 778 is an overlay area code for the Canadian province of British Columbia. It was created on November 3, 2001 as a concentrated overlay of area code 604...
over 250Area code 250Area code 250 is an area code for most of the Canadian province of British Columbia, including Vancouver Island. It was created on October 19, 1996 as a split of area code 604.The area code also serves the United States city of Hyder, Alaska....
in British ColumbiaBritish ColumbiaBritish Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
.
Number pool management
The persistent unpopularity of new area code creation, whether by split or overlay plans, led to a change in the rules of number block allocation, in order to conserve the pool of available phone numbers. This change, which allowed for the assignment of smaller number blocks, is commonly known as number poolingNumber pooling
Number pooling is a method of reallocating telephony numbering space in the North American Numbering Plan, primarily in growth areas in the United States....
. This has noticeably slowed the need for area code growth, but not completely. For example, the Western Washington
Western Washington
Western Washington is a region of the United States defined as that part of Washington west of the Cascade Mountains.It is known as being far wetter in climate than the eastern portion of the state, which...
area narrowly avoided needing an overlay in 2001. Area code 564
Area code 564
564 is a proposed area code for the state of Washington covering all of Western Washington, including Seattle. It would be an overlay plan for the 206, 253, 360, and 425 area codes...
, originally planned for introduction in October 2001, was canceled in August 2001 after state regulators determined that the existing number pool had begun to be used more efficiently.
See also
- List of area code overlays
- Interexchange carrierInterexchange carrierAn Interexchange Carrier is a U.S. legal and regulatory term for a telecommunications company, commonly called a long-distance telephone company, such as MCI , Sprint and the former AT&T in the United States...
- Telephone exchangeTelephone exchangeIn the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
- Telephone numbering planTelephone numbering planA telephone numbering plan is a type of numbering scheme used in telecommunications to allocate telephone numbers to subscribers and to route telephone calls in a telephone network. A closed numbering plan, such as found in North America, imposes a fixed total length to numbers...
- North American Numbering PlanNorth American Numbering PlanThe North American Numbering Plan is an integrated telephone numbering plan administered by Neustar which encompasses 24 countries and territories, including the United States and its territories, Canada, Bermuda, and 16 nations of the Caribbean...
- Exhaust dateExhaust dateIn telecommunications, an exhaust date refers to the date at which an area code will run out of numbers due to growth in the number of subscribers....