Apr 17, 2015 -- A detailed map of more than 280 million trees across England and Wales is helping the London Borough of Bromley prioritise its autumn street cleansing programme. As one of the largest London Boroughs, playing home to around two thirds of London’s woodlands, Bromley faces the annual challenge of clearing hundreds of tonnes of fallen leaves. Urban leaf fall can cause a hazard to the public by making pavements and roads slippery and potentially cause flooding by blocking drains and gullies. The National Tree map, created from Bluesky’s high resolution aerial photography, colour infrared data and detailed height datasets, helps the Council locate trees with close proximity to roads and pavements and identify large leaf species that have a greater contribution to the annual leaf fall.
“Bromley is a fantastic sight in autumn, having the highest number of trees across London, but there is a price to be paid and the challenge each year is to keep our roads and pavements as safe and clear of leaves as possible,” commented Luke Chittock, Systems Manager (GIS) at the London Borough of Bromley. “36,000 street trees together with park trees and school trees give a combined total of more than 100,000, with many more on private land. This volume of trees leads to acute leafing issues in the autumn with significant resources diverted to address the problem each year.
“Having worked with a sample of Bluesky’s National Tree Map, comparing it with our own tree asset database, we were confident that it would provide an efficient method of identifying the streets and pavements within the borough that had the highest concentrations of big leaf trees in order to prioritise our clean-up operation.”
The Bluesky National Tree Map data was analysed in conjunction with adopted street and path data from the Council’s National Street Gazetteer (NSG) and Ordnance Survey MasterMap data. This allowed for the surface area of maintainable streets to be established and the identification and location of attributes specific to different species. The end result was a table containing road name, NSG reference, road surface area, tree canopy area and big tree canopy area. This data allowed for the calculation of percentage canopy cover for any given street which was used to inform the leaf cleansing operation.
“By using this methodology we are able to make more effective use of our resources – targeting priority streets,” continued Chittock. “We are also able to respond more swiftly to customer queries as we have a scientifically based works list for our contractor in both tabular and cartographic form.”
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