what is greater manchester?
It is a metropolitan county and combined authority area in North West England.
Greater Manchester
Greater Manchester is a metropolitan county and combined authority area in North West England, with a population of 2.8 million; the third largest in England after Greater London and the West Midlands. 
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Greater Manchester [SEP] Introduction
Greater Manchester is a metropolitan county and combined authority area in North West England, with a population of 2.8 million; the third largest in England after Greater London and the West Midlands. It encompasses one of the largest metropolitan areas in the United Kingdom and comprises ten metropolitan boroughs: Bolton, Bury, Oldham, Rochdale, Stockport, Tameside, Trafford, Wigan, and the cities of Manchester and Salford. Greater Manchester was created on 1 April 1974, as a result of the Local Government Act 1972, and designated a functional city region on 1 April 2011. Greater Manchester spans , which roughly covers the territory of the Greater Manchester Built-up Area, the second most populous urban area in the UK.