New methods of creating UK Open footprint data
One of the greatest impediments to innovation in the UK in terms of sustainable city development continues to involve lack of access to open building footprint data.
All cities are made up of buildings. Like cells and atoms these constitute recognisable granular building blocks which collectively do much to determine a city's appearance, character, health and potential. Gathering data on a these buildings, and understanding the contribution of each to the city as a whole, is therefore critical for those involved in developing sustainable cities for the future.
Lack of discussion around this subject is largely a result of the difficulty in accessing building footprint outlines, required to store, analyse and visualise spatial metadata relating to the building stock.
A growing number of city authorities however, including those in the Netherlands, the US and Canada, are now releasing simplified building footprints and other metatdatasets at footprint level. This reflects an increasing global awareness of the value of granular information relating to the urban fabric, in enabling residents, government departments, visualisation specialists and those involved in research, education and business to innovate and to collectively solve urban problems, particularly those relating to the reduction of energy and the conservation of urban resources.
Below we see an example of the wave of stunning building age data visualisations (age data are essential in assessing rates of change in cities, building longevity and material stock flows) created by online developers across the world, using free software to merge building age and building footprint metadatasets.
These include Thomas Rhiel's visualisation of Brooklyn (below) which kick started the trend in 2013 following the release of NYC's PLUTO dataset. This was followed by Bert Spaan's visualisation of 9 million buildings in the Netherlands
http://code.waag.org/buildings/; Brandon Liu's million buildings in New York http://pureinformation.net/projects/building-age-nyc/ and most recently Ekaterina Aristova building age map of Vancouver
Courtesy Thomas Rhiel- Age of Brooklyn's buildings using NYC PLUTO data
Footprint problems in the UK
Ordnance Survey (OS) is the UK's main mapping supplier and began as a defence ministry operation in 1747. Over the centuries it has maintained its reputation as a producer of mapping of the highest standards and by the 1990s was considered to have the most advanced digital mapping service in the world.
However in recent years, largely as a result of ongoing pressure from central government to maximum profits from commercial products, OS has failed to keep up with the world's open mapping movement. Despite recently releasing a number of open datasets, the most detailed, OS Open Map Local (2015), only offers vectorised polygons at streetblock level. As such OS products cannot currently be used to collect, visualise and release citywide metadata nor tap into into our ability to generate new metadatasets relating to the city's fabric though crowdsourcing knowledge.
In 2004, in response to the absence of OS open footprint data Steve Coast initiated Open Street Map (OSM). This free product,created for and by the community, now has worldwide reach, and has had not only a profound influence on the debate over open mapping, but has also demonstrated the urgent need for it.
However over a decade has passed since OSM's appearance, and despite considerable energy expended by the OSM community in the UK, building footprint data is still piecemeal. Meanwhile OS's only vectorised building outline product, MasterMap, continues to remain prohibitively expensive for many, with licences also heavily restricting online use.
Accelerating the release of comprehensive open building footprint data for the UK.
At CASA we are looking at ways in which to accelerate the release of Open footprint data for the UK in order to facilitate greater innovation in the debate around city sustainability. Our approach is to build on the availability and advantages of the OS Open Map Local product (currently in beta form) and to tackle its key weakness, its lack of block subdivisions. OS Open Map Local, covers the whole of the UK, is derived from highly reliable OS data and has the potential to be easily updated. It therefore has a number of advantages over OSM where all new blocks and buildings must be created from scratch and where systematic updating is not possible.
Our aim has been to find a way of subdividing blocks as quickly and accurately as possible to create simplified building footprints, less detailed than MasterMap but more detailed than say the LIDAR derived footprints released for Vancouver. To then release both the methodology and open samples online, and with these test methods of crowdsourcing, analysing, visualising and releasing building fabric related metadata.
This will enable us to demonstrate to OS and central government the value of updating OS Open Map Local to include simplified building subdivisions, and at the same time allow local, and professional, communities
to get on and create and release open metadata themselves.
Our method simply involves taking OS's Open Map Local and adjusting and subdividing the vectorised polygon blocks using the OS National Grid (NG) 1:2500 1943-1995 series, 1950s tiles (for pre WW11 buildings), with Bing aerial images used for postwar buildings.
NG 1950s tiles are over 50 years old and are therefore out of copyright. No restrictions apply where maps are owned by the user and vectorised data derived from these, along with raster images, may be uploaded online. These may be purchased as originals from map suppliers or as raster tiffs from Landmark Information Group, an independent company set up in 1995 https://www.ordnancesurvey.co.uk/business-and-government/partners/finder/landmarkinformationgroup.html.
(Annual licence restrictions apply for maps under 50 years old). Estimates are provided on application however the costs for base data to outline around 2,500 buildings in our inner London test area is approximately £170.
Where historical map scans are accessed via a licence agreement, as for UK universities via Edina Digimap, scans cannot be uploaded. Though we understand from OS via Edina that new vectorised material can be derived from Edina historical maps for small areas we await confirmation that the release of vectorised data for large areas, ie whole cities,using out of copyright maps is not restricted. Our argument is that there should be no restrictions as the proposed process involves the production of new artworks involving the tracing of only partial building outlines from maps over 50 year old.
In the current trial a sample of 2,500 buildings in Archway, Islington, London, was vectorised in a day and half, using the Edina Digimap NG 2,500 1952-54 map tiles (shown below). Around 70% of the party walls of the sample stock matched those from the 1950s though minor alterations to extensions (ie removal of outside lavatories, or additional extensions) had often occurred. Arc Scan was not employed on this sample owing to the small sample size and clean up time involved, though its value will be assessed.
Created using OS Open Map Local 2016. Basemap Edina Digimap NG 2,500 1943-1995 map tiles.
Bing satellite and birdseye imagery were then used to subdivide post 1954 stock. Where individual entrances could be detected and where rooflines were subdivided, polygons were split. This was done by estimating footprint by block length and number and regularity of subdivisions, rather than tracing, to ensure that any possible future restrictions imposed by Bing ( a key resource used by OSM) would not affect the open nature of the vectorised data. For most cases postwar stock comprises social housing developments where subdivisions are identical across multiple blocks. Those buildings containing flats with single entrances were left as single polygons.
Once complete the open footprint map with provide a free resource for individuals, organisation, institutions including schools, and businesses within the local community from which unlimited and unrestricted digital and paper copies may be made. This will enable online crowdsourcing, analysis of metadata, and an assessment of the value of these data in the context of sustainability, to proceed.