Geography Reference
In-Depth Information
stock; the data may apply only to particular sectors of the housing stock (e.g. the public
sector); the data are not available for individual properties but as counts for an area; the data
do not include the information required by the local authority; collecting the data is often
very expensive and time-consuming, even for a sample of the housing stock. In addition,
even in a stable housing market properties are constantly changing. People die or move
away and the property is passed on. Old properties are demolished or abandoned and new
ones are built. The use of properties can change, from residential to commercial and vice
versa, or they are sub-divided or amalgamated into new dwellings. All these factors mean
local authorities and quite often central government departments can have poor quality
information on individual properties. For instance, although the British Valuation Office
Agency (VOA) holds the most extensive set of property attribute data in the UK, the vast
majority of these data are held on paper records (VOA, 2002a) making them both difficult
and costly to access and maintain.
Government departments are therefore looking towards new techniques for collecting
property information and high-resolution aerial photography is increasingly being pro-
moted and used as an important source of such data. In conjunction with high-resolution
GIS framework data and other ancillary data sources, aerial photography can enhance exist-
ing dwelling data and provide new information (Orford and Radcliffe, 2007). Methods are
being developed that can extract building information automatically from aerial photogra-
phy, such as building footprints, roof types and photogrammetric measurements (Elaksher,
Bethel and Mikhail, 2003). Aerial photographs can also show how the property fits into
the landscape and relates to its neighbours. Crucially, these data can be collected relatively
cheaply and unobtrusively as Diane Leggo, director of local taxation at the VOA, has re-
cently commented: 'aerial photography and photogrammetry matched with geographical
positioning systems [allow] significant data gathering without inspections' (cited in the
Daily Express
newspaper, 29 May 2006, p. 9).
This data gathering 'without inspections' means that aerial photography is a very effective
method of gathering property information in rural and sparsely populated areas. Here, it
can be often too expensive to undertaken conventional property surveys due to the distances
involved in travelling between properties. Instead, high-resolution aerial photography can
provide the necessary information for a fraction of the cost. Harper (1997) discusses how
aerial photographs can provide insights into the nature of rural areas by revealing subtle
features which are not apparent from ground level. This can include properties hidden
from view that have been built without planning permission or building permits but can be
identified on aerial photographs. Even in more densely populated areas, aerial photography
can show features of a property that may not be apparent from a visual inspection from the
road, for instance unreported improvements such as a new garage or swimming pool. Aerial
photographs can also allow the visual analysis of the rear elevation of a property rather than
simply the front elevation, which is characteristic for physical surveys. As will be discussed
later, these uses can have important relevance in respect to local taxation issues and also
issues relating to privacy.
Aerial photographs are especially useful in places where very little property data, or indeed
any socio-economic data, exists such as in the developing world (Corker and Nieminen,
2001). Here, they are often used to map buildings, chart development and provide a basic
enumeration of population. A topical example in this area is the recent work on charting the
global growth of gated communities, a phenomenon that is occurring in many countries.
Aerial photographs are good at showing the dimension and borders of gated communities
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