To avoid any confusion, Manchester in this case means the City of Manchester as opposed to Greater Manchester. For people outside the conurbation this seems a continuous source of confusion; people often ascribe events in Salford, Bolton, Trafford etc to 'Manchester'.
The Green Party functions as Local Parties, (not 'branches, please) each of which occupy a geographical area based on one or more local authorities or constituencies. Manchester Green Party currently has the rather complicated area of the City of Manchester plus the constituency of Salford and Eccles. There are thriving Green Parties in the neighbouring metropolitan boroughs of Trafford, Tameside and Stockport , whilst South Lancashire Green Party (for now) covers the rest of Salford, Bolton, Bury and Wigan.