We often get asked questions like; how many tall buildings are there in London?
On the face of it, this may sound like a simple question, but the answer is not so straight forward. First, we must break down the question and identify the different elements within it.
1. What do you mean by London? Greater London, The City of London, The area within the M25…
2. What is tall? More than six 6 stories, more than 18 metres high…
3. What is a ‘building’?
Points one and two are usually resolved easily although defining some urban areas is challenging.
However, point three – what is a building? - is more difficult. This may not seem a problem, but actually, different interpretations can have a significant impact on the answer. As the image below shows, Buildings can be complex and how we refer to and reference them reflects this.
Terms such as Building, Property, Premise, site and even Address are often used interchangeably and may refer to everything from groups of buildings, to a small part of a specific building. In the UK, a wide range of identifiers are used to reference these Buildings, Properties, Premises, Addresses…as has been highlighted in Owen Boswarva's blog.
Geomni both capture unique building data and, increasingly, incorporate third party datasets into our property mapping solutions. Matching these disparate datasets is also greatly impacted by the definitions used.
When talking with clients we always start with some clear definitions to ensure everyone is fully understands the terminology.
For Geomni a ‘Building’ represents the ‘footprint’ as defined by the continuous perimeter of a structure. So, a terrace of houses or pair of semi-detached homes are one building:
Where we can identify divisions, we divide ‘Buildings’ into ‘Premises’: a whole or part of a building with a consistent use, owner or occupant.
A Premise or building can be made up of different ‘Elements’: a subdivision of a building which identifies a difference, usually in terms of height or classification.
We use the concept of a site which groups buildings together, an area of land identified by physical features that create a boundary, or an area of consistent land use or ownership for example, all the buildings that comprise a school; or, as below, group domestic outbuildings with the premise:
We also include address references in our building data solutions. This takes the form of a Unique Property Reference Number, UPRN, now available as Open Data, see Improved access to MasterMap data and core location identifiers. Much building data is referenced to an address, for example Energy Performance Certificates, and increasingly UPRNs, for example HMLR Lease information.
To make the most of this wealth of data, and to make integration of datasets easier, we maintain the relationships between buildings, premises, sites and UPRNs (addresses). The relationships are complex with many-to-many relationships between them:
By maintaining all of these complex relationships, and others such as Ordnance Survey TOID identifiers, we can present the building data that we capture in whichever way our customers need to answer their questions.
So, in answer to our original question, within Greater London, the administrative area governed by Boroughs there are approximately 42,000 “buildings” greater than 18m high, 44,000 “premises” and more than 700,000 “addresses” associated with those buildings.
Which answer do you prefer?