Do you know what percentage of your borough is covered by trees and woodlands? Do you know if it has changed significantly over the time or how it varies within different parts of your borough? Without knowing your existing tree cover, how will you plan and manage future tree planting?
To answer these and other questions, the LTOA would like all London boroughs to complete and return a baseline canopy cover survey. In order to achieve this, the LTOA with the support of the Greater London Authority, have devised a straightforward means of estimating tree canopy cover. The tools we have created are called ‘OSCCA’ (Open Source Canopy Cover Audit), and are available for anyone to use. OSCCA allows you to generate random points on aerial images of your borough, which can then be classified according to land cover, (trees, roads, water, etc). This quickly lets you build up a reliable tree canopy cover estimate.
There are two sets of guidance for OSCCA to help you to undertake your canopy cover survey. Which guidance you follow depends on the mapping system in use in your borough, either ArcGIS or MapInfo. If you are unsure which system you use then please speak to a colleague in your mapping team.
It is important that you check the licence arrangements for your aerial images with your colleagues in the mapping team, as some licence restrictions may prevent data (such as canopy cover), being derived from aerial imagery and made public. If you are in any doubt about the licence arrangements for your aerial photographs you can contact the Greater London Authority, who are able to make aerial images available to London boroughs to use in this project without this licence restriction.
Once it is set up, the canopy cover survey is quick and easy to complete. And when you have completed the survey you can:
- Compare the percentage of trees and woodlands with other green infrastructure, or with the percentage of land covered by buildings or transport infrastructure for instance.
- Use the survey results alongside other datasets (such as ward boundaries) to determine areas of low canopy cover to prioritise locations for new tree planting.
- Assess the difference that recent tree planting has made to your canopy cover, by repeating the survey using past aerial images.
- Record and monitor progress on meeting targets for canopy cover.
- Take on more complex surveys – for example distinguishing between privately and publicly owned trees
Members of the Canopy Cover Working Party are:
- Rupert Bentley-Walls (London Borough of Hackney)
- David Houghton (London Borough of Camden)
- Dave Lofthouse (London Borough of Merton)
- Barbara Milne (City of Westminster)
- Jonathan Robinson (London Borough of Hackney)
- Matt Thomas (Greater London Authority)
The programme for MapInfo was created by Jonathan Robinson (London Borough of Hackney).
The guidance for using ArcGIS was devised by Matt Thomas and Rebecca Page (Greater London Authority).