Greenkeeper defines four size groups (pocket park: under 0.4 ha; small open space: between 0.4 ha and 2 ha; local park: between 2 ha and 20 ha; district park or larger: larger than 20ha). The size definitions are based on guidance from the Greater London Authority, which can be found at current London plan. The size categories are used to compare visit numbers and values of benefits of a greenspace within its peer group.