While the Golden Horseshoe would have likely needed another area code due to its continued growth, it is very likely that the immediate need for relief would have been staved off had it been possible to reallocate numbers from the smaller rate centers in the region to Metro Toronto. Within two years of the 905 split, 416 was back on the verge of exhaustion. American cities such as New York City, Chicago, and Los Angeles had been split between two area codes, but that solution was quickly ruled out for Metro Toronto because of the area's extremely dense population and the lack of a suitable boundary for a split. It was ultimately decided to overlay 416 with area code 647 in 2001, two years after Metro Toronto was merged into the "megacity" of Toronto. The successful implementation of 647 triggered the rapid adoption of overlays across Canada. By 2013, seven-digit dialing had been eliminated in every Canadian numbering plan area except in the country's three Arctic territories (area code 867), a large but sparsely-populated area in northwestern Ontario (area code 807), New Brunswick (area code 506), and Newfoundland and Labrador (area code 709). Overlays are now the preferred method of expansion in Canada, and no numbering plan areas have been split in the country since 1999. British Columbia and the Prairie Provinces have followed Puerto Rico and West Virginia's lead with province-wide overlays. In those cases, a factor behind the decision was the desire to spare rural areas the expense and burden of changing their numbers. Types The North American Numbering Plan Administration recognizes several types of overlays: In a distributed overlay, or all-services overlay, an entire existing area gains another area code serving the entire area. Most 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 area codes, but all of them have since covered entire areas. In a multiple concentrated overlay, the entire existing area gains multiple additional area codes, each of which serves a different subsection of the original. This has not been implemented yet. In a multiple-area distributed overlay, two or more numbering plan areas gain a single new area code covering such the entire area, either concurrently or in phases. Examples include 872 in Chicago, Illinois (over 312 and 773) as well as 587 and