International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
topographic database and 5,000 updates are applied every
working day. This is provided as the foundation for all other
information and is based on the National Grid coordinate
system. A transformation [OSTN02] now defines the OSGB36
National Grid in conjunction with the ETRS89 positions of the
National GPS Network stations.
Since then, other layers have been added: the roads components
of an Integrated Transport Network, colour orthoimagery and
all 26 million postal addresses georeferenced to better that 1m.
All of these, except imagery at the moment, cover the entire
area of England, Wales and Scotland [234,410 Km°]. Further
layers are being developed or will be migrated in the near
future.
A consultation paper on the concept of DNF and the methods to
support usage was published in early 2000 [Ordnance Survey,
2000]. Since OS MasterMap was released take up of the
concept has been steady and the adoption and evolution of the
methods has been progressing. Several successful projects have
been completed, such as the development of a new national
database recording and showing all land open to public access.
In the light of this experience and further work at national and
international levels, a further White Paper on DNF will be
published in 2004.
4.2 The Concept
“The Digital National Framework (DNF) provides a
permanent, maintained and definitive geographic base to which
information with a geospatial content can be referenced"
[Ordnance Survey, 2000] and incorporates:
*.a set of enabling principles and operational rules that
underpin and facilitate the integration of geo-referenced
information from multiple sources”
DNF is broader that the national mapping agencies data, other
organisations contribute to the framework and all kinds of users
can create their information on the maintained base with greater
confidence and assurance. Clearly change in process and
practise will be required to achieve this and a stepped approach
to adoption (the “levels” described later) has been developed to
support this.
4.3 DNF principles
DNF is supported by four guiding principles:
|. The detailed ground rules shall be driven by the
strategic needs of the wider GI community.
2. Data should be collected only once and then re-used.
J
Reference information/data should be captured at the
highest resolution. Information may then be published
via a) different representations at scale b) multi-
resolutions across scales - to meet different application
needs.
4. DNF will incorporate and adopt existing de facto e.g.
OpenGIS and de jure standards e.g. ISO, wherever they
are proven and robust.
Therefore DNF is not an Ordnance Survey strategy; it is aimed
at providing a better framework for all users of GI in Great
Britain. While it will not necessarily be appropriate everywhere
its adoption, partial or otherwise, would be welcomed and the
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experience could help with current European initiatives such as
INSPIRE [European Commission 2004] and EuroSpec [Luzet
& Land, 2004].
4.4 Reference data and Applications data
Already this paper has recognised that reference information is
not the sole domain of NMCA’s and there will normally be
several other organisations that might contribute to the
framework. The methods will be published in the public domain
and maintained. Therefore the framework is inclusive in nature
and open in the way it can be used by the industry at large.
Figure 2. The relationship of Framework and Application
Information
The world is not so black and white in terms of Reference and
Application data. There will be shades of grey in the boundary.
For example a base topographic (or cadastral) map will
underpin a land registration system. The parcels defined in that
system are therefore at the “application” level. However this
information is itself often used as a reference feature for other
information that may be shared across organisations. Therefore
Reference Information will evolve and will be defined by usage
by several parties for linking their Application data or
information. In the DNF model, any further information which
is definitive, and is a) used widely for referencing and b)
associated with the Base Reference Information is known as
“Associated Reference Information". Table 1 below illustrates
the different types of information that broadly fall into these
three categories.
4.5 Georeferencing
The heart of DNF is the provision of a coherent georeferencing
system. One that is both extensible and inclusive. Inclusive in
the sense that many organisations may contribute to the
referencing framework and it is also open to all those who wish
to reference their application information to it, and then share
and exchange their information with third parties or exploit it
commercially. All parties who have invested in creating and
maintaining such data are likely to wish to secure that and
future investments by protecting their information in some way
to ensure that its future is sustained.
The georeferencing framework is based on giving each object in
the landscape a unique identifier. This is known as a TOID and
is a sixteen digit unique number, bearing no intelligence. Each
building in OS MasterMap is referenced by a TOID as is every
other feature such as fields, woodland, street segments etc.
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