[October 19, 2001] Through its XML Schema Repository, the UK Digital National Framework (DNF) has released a number of draft XML schemas supporting the Ordnance Survey's geographical database. The schemas are based upon extensions to the GML version 2.0 specification.

The Digital National Framework (DNF) "is a definitive, consistent and maintained framework for the referencing of geographical information in Great Britain. It comprises the National Grid linked to Global Positioning System (GPS), height data, detailed topographic information and unique identifiers on features. Key elements are: (1) Polygons: the building blocks of our data representing real world features; (2) Maintained topographic identifiers (TOIDs) on all features; (3) Seamless data; (4) A themed classification based on the real world; (5) Availability of data by themes; (6) Metadata on each feature..."

Vanessa Lawrence (Director General and Chief Executive, Ordnance Survey's Digital National Framework) indicated that the DNF data will be issued in geography markup language (GML) format (a new international standard for storing and transporting geographical information), initially "layered into nine themes: buildings; structures; roads, tracks and paths; land; administrative boundaries; water; heritage; height; and rail. The database will offer complete seamless coverage of the whole of Britain; in addition, it will give users the ability to select not only the precise geographical area of coverage they needed but also only those themes -- such as roads or buildings -- they require from the data... around 400 million features in the new database had been allocated unique topographic identifiers (TOIDs) which will dramatically ease the task of associating different datasets from other sources to the Ordnance Survey material... the complete database includes identifiers for every feature, including individual fields, lakes and even pillarboxes... the is already used, for example, by the police to catch criminals, motorists to plan journeys with in-car navigation, and insurance firms to calculate risk. It is of growing importance in commercial marketing, business analysis, location-based services and in the delivery of efficient public services... [the research teams have] converted all 230,000 of the most detailed point-and-line Land-Line mapping tiles to a seamless data source containing 400 million self-contained individual objects... Data from the Digital National Framework is designed to be Internet- and customer-friendly, making it even easier for public bodies and businesses to pick and mix the mapping and geographical information they need..." [see news item]

The draft DNF Release 1 product data specification includes XML schema documents, a specification overview, classification and attributes of DNF features, DNF themes, lifecycles of DNF features, DNF geometry and topology, DNF data in GML, and a DNF glossary.

From "DNF Data in GML": [This document supplies a] description of how DNF data is represented in the Geography Markup Language; it defines how Ordnance Survey data available within the Digital National Framework (DNF) is represented in the Geography Markup Language (GML) version 2.0. This document is primarily for system developers who are writing software that uses such data.. Explanations of how we manage complex properties and polygon based topological relationships in our application schema are provided in the relevant sections of this document... The DNF application schemas "define four main types of properties that are present inside a feature element. These are simple, complex, geometric, and topological properties. The ordering of properties within a feature element is important as XML validation is reliant on elements being in a specified order. The order of properties is specified within the XML schema. (1) A 'simple' property is one that contains a single piece of non-geometric information. These properties correspond to the simple DNF feature attributes defined in the DNF Specifications document Classification and attributes of DNF features. The value of each DNF feature attribute is enclosed in an element that takes its name from the DNF feature attribute... A feature association is a simple property that defines a relationship between one feature and another, for example, an administrative boundary could maintain a relationship to a topographic feature such as a stream that defines the boundary... (2) A complex property is one that contains more than one piece of information. These properties correspond to the complex DNF feature attributes defined in the DNF Specifications document Classification and attributes of DNF features. The complex property element takes its name from the complex DNF feature attribute. Each part of a complex property shall be encoded as a simple, feature associations, complex, geometry or topology property, as appropriate inside the complex property element... (3) A geometric property is one that describes a specific geometry. We have extended the GML v2.0 specification to include a rectangle that is defined by two points. The first point defines the minimum co-ordinate whilst the second point defines the maximum co-ordinate. All geometric properties are encoded by placing the GML geometry elements inside an element that takes its name from the DNF feature attribute. The XML attribute srsName shall be set to osgb:BNG (British National Grid) which uses eastings and northings specified in metres... (4) The document seeks only to describe the XML encoding of topology. For details on how this is used to represent DNF features, see the DNF specification document DNF geometry and topology..."

From the specification overview:

Detailed digital data derived from large-scale topographic surveys is part of the Ordnance Survey Digital National Framework (DNF). This is the first topographic data product to be released in the DNF programme. The DNF provides a topographic referencing framework for Great Britain. The purpose of the data is to support a wide range of applications dependent either directly or indirectly on geographical data, including: (1) geographical analysis; (2) geographical referencing; (3) feature management and feature attribution (data association); and (4)cartographic representation.

National coverage of this product contains approximately half a billion features. DNF features are representations of many types of topographic real-world objects in Great Britain including buildings, roads, track, paths, railways, rivers, lakes, ponds, and structures such as oil storage tanks and pylons. The data also includes non-topographic features such as administrative and electoral boundaries. These objects are represented digitally as point, line, area, symbol and text features, each with attributes that give more information about the feature.

DNF data is designed for use as an intelligent digital map within GIS and database systems. In DNF data there is a closer correspondence between data features and discrete real-world objects than has been the case in previous generations of Ordnance Survey products. The life cycle of each feature is matched, as far as is possible, to that of the real-world object(s) that it represents. The main exception to this principle is the life cycles of line features, which are constrained by topological structuring rules and so cannot always follow the life cycle of the real-world objects they represent.

Every DNF feature has a topographic identifier (TOID). This is a 16-digit integer that uniquely identifies that feature. Each feature also has a version number which is incremented each time there is change of any kind to the feature in the Ordnance Survey database. Each DNF feature has several descriptive attributes, including one or more descriptive group, and optional descriptive terms. These attribute values are reflected in the 5-digit feature code of the feature. DNF data also includes inferred links, which are non-topographic line features inserted to improve the subdivision of area features, in situations where physical boundaries do not serve this purpose. Inferred links represent inferences about the real world based only on the topographic map information, not on any other sources of fact. Inferred links are normally used to: (1) Divide roads into sections at junctions. (2) Separate individual garden plots in residential areas where no dividing fence, hedge or wall has been captured in the topographic data. (3) Divide roads from car parks and hardstanding areas. (4) Close fields which have gaps in their boundaries. (5) Define the edge of the extent of a named area (for example, the edge of a playing field).

[July 09, 2001] Testing 2001-Q3: "Early Adopters E-Delivery Testbed. Between mid July 2001 and November 2001, Ordnance Survey will be operating an online service known as the Digital National Framework (DNF) E-Delivery Testbed. The Testbed will enable customers to trial some features of the first national release DNF product and service (DNF version 1 release 1) which will be available in November 2001. The Testbed will give access to a selection of DNF test data and provide an experience of the online ordering process similar to that planned for DNF version 1."

Ordnance Survey is a UK government agency "which signed a seven-year agreement with the British Government to provide improved mapping services needed in the national interest. Key provisions include the acceleration of the updating of detailed maps of rural areas and major improvements to Ordnance Survey's national computer database. Resources are also being provided to speed work on national coverage of a new generation of both 1:10,000-scale and 1:25,000-scale mapping, and there is investment to ensure that details of all administrative and electoral boundaries in Britain are kept up to date. Other provisions include the recording of Welsh and Gaelic names on maps and the creation of a three-dimensional geographical positioning network for Britain, integrating information on the ground with that provided by orbiting satellites."

References:

• Digital National Framework (DNF)
• Digital National Framework (DNF) XML Schema Repository
• DNF Product specification. May 2001 or later.
• DNF Specification Overview. Version 1.0, First issue. May 2001. Document ID: d00506.doc. 16 pages. [cache]
• DNF Data in GML. 12 pages. [cache]
• DNF XML schemas:
  • OSDNFFeatures.xsd provides a definition of the features and their properties used within the DNF. [cache]
  • OSGeometryTopology.xsd defines geometry and topology extensions to the GML 2.0 specification as required by Ordnance Survey. [cache]
  • OSQueryresult.xsd provides the definition of a query result within the DNF. [cache]
  • OSSimpleTypes.xsd defines the basic enumerated types used within the DNF including 'descriptiveGroupType' and 'accuracyOfPositionType'. [cache]
• Classification and attributes of DNF features [cache]
• DNF themes [cache]
• Life cycles of DNF features
• DNF geometry and topology
• DNF glossary
• README for draft DNF Release 1 product data specification
• DNF Report (2000)
• Contact: dnfinfo@ordsvy.gov.uk
• Contact: Tony Harvey (DNF Data Specifications Manager).
• See also: "Geography Markup Language (GML)."