These Technical Notes accompany the Green Space Index and supplement the published Frequently Asked Questions with more detail on how the Index has been calculated and compiled.

We continue our work to develop and expand the Green Space Index and would welcome any comment by email to info@fieldsintrust.org.

The aim

Through the Green Space Index we analyse publicly accessible local park and green space provision within Great Britain. The Index follows on from our Revaluing Parks and Green Spaces research released in 2018 and supplements our wider policy work in the parks and green spaces sector. The May 2019 release of the Green Space Index was the first time such a measure had been published to take stock of the quantity of local park provision across Great Britain and the annual updates support our evidence-led approach calling for parks and green spaces to be revalued for the benefits they contribute to society. We believe that green spaces are good, do good and need to be protected for good.

Having established baseline data through the May 2019, 2020 and 2021 releases of the Green Space Index, future iterations of Ordnance Survey's Open Greenspace product and updates to population via the Census and projections will enable us to track trends in provision over time.

Scope

The Green Space Index covers Great Britain and analyses publicly accessible local park and green space provision as mapped by Ordnance Survey, with a more detailed discussion below of how their data is used. Not within the scope of the Green Space Index is regional park and green space land, such as national parks and common land, or other aspects of green infrastructure such as canal towpaths and grass verges.

Northern Ireland is not included in the Index because park and green space data is not made available by Ordnance Survey of Northern Ireland. If such data becomes available in the future we will look to expand the Green Space Index to cover the province.

Green Space Data

The Green Space Index is compiled using the OS Open Greenspace product, with the May 2022 release of the Index using the April 2022 release of OS Open Greenspace.

Within the OS Open Greenspace product we use the site extent polygons in all cases. From the site extent layer we exclude four typologies which are not deemed to be within scope of the Green Space Index. The excluded typologies are: Allotments & Community Growing Spaces; Cemetery; Religious Grounds; and Golf Course.

Typologies which are within our scope and which have been retained for analysis are: Bowling Green; Other Sports Facility; Play Space; Playing Field; Public Park or Garden; and Tennis Court.

We have also removed three areas of land, detailed below, which appear within the dataset but we do not deem to be within scope. We are reliant for the Index on the dataset published by OS and have not performed a nationwide review of the accuracy of this data as it is not within our scope to do so, but do believe these examples to be indicative of errors which may currently exist within the data. These have been fed back to OS, who are accepting feedback on errors within the data as they continue their verification process. We will continue to work with them to support this process where we are able.

Land removed from in-scope typologies as not deemed to be within scope of Green Space Index:

• 9E891041-3B3D-2C71-E053-A03BA40A7146 - Whinlatter Forest Park
• 9E89103E-2B7F-2C71-E053-A03BA40A7146 - Rutland Water
• 9E8911BB-0CE6-2C71-E053-A03BA40A7146 - National Cycling Centre

Within the Ordnance Survey Open Greenspace data there are instances of spatial overlap which results in duplication of park and green space areas and has the potential to skew our Green Space Index calculations. These overlaps fall into two categories:

• Overlap where small features have been overlaid on larger features.
• For example a polygon representing a play area sitting on top of a larger polygon representing a park. This leads to double-counting of the area of the play area. We have run analysis to identify areas of overlap and erase the area of the smaller feature from the larger feature, thus removing double-counting but retaining the mix of typologies that may exist on a space.
• Duplication of entire polygons where two or more identical polygons sit on top of one another.
• Common examples of this are a polygon representing a tennis court layered on top of or below an identical polygon representing an other sports facility. We have controlled for this by analysing identical polygons and only retaining the first one listed within the dataset.

Therefore we have taken every effort to remove all instances of overlapping and duplication from the data as accurately as possible within our scope. As previously noted we are reliant on the dataset published by OS and will continue to work with them to support their verification process where we are able. We have noted accuracy-related revisions between the April 2020, April 2021 and April 2022 releases of the OS Greenspace data and it is for this reason we do not yet feel able to draw comparisons to the findings of the first two releases of the Green Space Index. If you find any inaccuracies whilst browsing the OS Greenspace product you can report these using the contact form on the OS website, selecting "Map errors and omissions". We are also committed to working closely with Ordnance Survey to improve green space data across the UK especially with regards to existing legally protected spaces.

Other data used in the Green Space Index

Population projection data
Whilst the majority of the Green Space Index is compiled using the OS Open Greenspace product, some measures are calculated by combining analysis of this with population data.

For the May 2022 release of the Green Space Index we have in all instances used data for the projected 2022 population, to provide a more accurate product. This is a change from the May 2019 release of the Index in which we used data from the 2011 Census.

For the population figures for 2022 and beyond, we used data provided by Geolytix, who specialise in data and demographics. The projections for years beyond 2022 are modelled from a household first perspective. They use OS address data and combine data on all large-scale planning developments with Census data on household compositions. This is done at postcode and Output Area level, but the figures are then constrained to 2016-based ONS population projections at local authority level.

In analysing the impact of projected changes in population of green space per capita, we used the projections data calculated by Geolytix. They have used the above methodology to provide the projections up to and including 2025 and for projections beyond 2025 apply change at local authority level in 2016-based ONS projections to give precise projections at local authority and national/regional level. We have not analysed effects of changing population below local authority level beyond 2025 as this data is not considered reliable at such a granular scale for such timeframes.

Geographic and statistical boundaries
When visualising data we have produced a single WebApp for Great Britain. Within the App we use 2011 Lower Layer Super Output Area (LSOA) boundaries for England and Wales and 2011 Data Zone (DZ) boundaries for Scotland. All analysis and calculations to compile the Index and data for display in the WebApp has been carried out using full resolution clipped boundaries. To aid load times and provide as smooth a user experience as possible, however, we have presented the data on the WebApp using generalised boundaries.

Attributions and credits

The Green Space Index is compiled using National Statistics data © Crown copyright and database rights (2022), NRS data © Crown copyright and database rights (2022), OS data © Crown copyright and database rights (2022) and Royal Mail data © Royal Mail copyright and database rights (2022).

We would like to place on record our thanks to Esri UK, Geolytix and Ordnance Survey for their continued support of our policy and advocacy work.