From the Wikipedia page 
The West of England Combined Authority is a combined authority within the West of England area, consisting of the local authorities of Bristol, South Gloucestershire, and Bath and North East Somerset. The combined authority is led by the Mayor of the West of England. The first election for this post took place in May 2017, when the Conservative candidate Tim Bowles was chosen on a turnout of 29.7%.
Devolution of certain powers to the West of England was announced in the 2016 budget. The government's vision was to create a "Western Powerhouse" analogous to the Northern Powerhouse concept. The proposal could bring nearly £1 billion of investment to the region over thirty years.
The original proposal was to cover the same area as the County of Avon which came into formal existence on 1 April 1974 and was abolished in 1996. However, in June 2016 North Somerset council rejected the proposal. Bristol, Bath and North East Somerset and South Gloucestershire councils agreed to progress with the proposal.
The West of England Combined Authority Order 2017 came into force on 9 February 2017. The first public meeting of the combined authority took place on 1 March 2017 with an interim chair.
The region covered by the authority had a population in 2015 estimated at 1,119,000 (which according to the reference also includes North Somerset).