OS MasterMap^® Address Layer 2 data quality

The quality of OS MasterMap Address Layer 2 data is specified by the themes and the ID cross-reference table identified within the technical specification document.

Go to the OS MasterMap Address Layer 2 detailed product information page to download the technical specification.

Within each theme, data quality is then considered against the relevant data quality elements in accordance with ISO19113 Geographic information quality principles (2002) and the Address Layer 2 specification defined within the technical specification.

Ordnance Survey will periodically review the data collection processes and measure the quality of the OS MasterMap Address Layer 2. As Address Layer 2 matures a richer catalogue of measures will become available. Subsequently the information provided on this web page will be developed and updated.

1. Completeness

Address theme

Definition

Completeness of the address theme is defined as the correspondence between OS MasterMap AddressPoint features (all match statuses) and the Royal Mail^® Postcode Address File (PAF^®).

2. Temporal validity (currency)

The OS MasterMap Address Layer 2 product is regenerated on a six week cycle. The datasets supporting it are continually updated.

Objects without postal address (OWPA) theme

Definition

OWPA theme currency is dependent on our ability to capture and classify new features within our topographic dataset and then make them available in the OWPA theme.

Topographic dataset currency of significant detail is measured:

*The definition of category A change can be found in the OS MasterMap user guide.

Go to the OS MasterMap user guide page.

3. Positional accuracy

Address theme

Definition

With regard to an address record, the positional accuracy is relative to the position of the feature to which it refers. ISO19113 defines relative accuracy as positional consistency of a data point or feature (OS MasterMap Address Layer) in relation to other local data points or features within the same or another reference dataset. In this case the reference dataset is OS MasterMap Topography Layer.

The measurement of the positional accuracy of addresses also takes into consideration the position metadata.

4. Attribute accuracy

Definition

How accurately the attributes within the dataset record the information about objects against either reference datasets or the real world.

Address theme

MOWPA theme

5. Logical consistency (all themes and cross-referencing table)

Definition

Format consistency: how closely the data stored and delivered fits the database schema and agreed supply formats.

Lineage (data quality dependencies)

External datasets

We are dependent on the quality of all the source datasets that are incorporated within the address infrastructure. In particular, we rely on third party data completeness, currency and attribute accuracy. Whilst we are not directly responsible for these elements within the address infrastructure, we have a responsibility to validate all information supplied to us. The more datasets incorporated, the more ‘definitive’ datasets we have to validate against. Where anomalies are identified the relevant third party will be fed back information to correct data. In this way we can improve the quality of all source datasets and, ultimately, the quality of the address infrastructure and the products derived from it.

OS MasterMap datasets

Other OS MasterMap datasets impact on the overall quality of OS MasterMap Address Layer 2. Therefore to understand the overall quality of Address Layer 2 one must also consider the quality of these datasets.

• OS MasterMap Topography Layer provides the position to which addresses relate.
• OS MasterMap Integrated Transport Network^TM (ITN) provides street information that build the address of OWPA features and help corroborate and match against addresses received from external parties.
• OS MasterMap Topography Layer provides the text-associated features that form the basis for the creation of the OWPA theme.

The most important quality elements of both the Topography and ITN Layers that can affect the quality of Address Layer 2 are:

• completeness (do all the necessary features exist in the dataset?);
• currency (is the dataset up to date?); and
• attribute accuracy (is the feature correctly represented?).

Other OS MasterMap datasets

Additionally, the BS7666 addresses within the product have field attributes that are derived from additional datasets and products:

‘Locality’ attribute – based on parishes (England and Scotland) and communities (Wales) in the 1991 Ordnance Survey Boundary-Line^TM dataset, and further updated using electoral districts and wards from the 1992 Ordnance Survey Boundary-Line dataset. This data is frozen and historical for several reasons. Firstly, this was the last time Scottish parishes appeared in the dataset. Secondly, whilst parishes have been substantially renamed this dataset represents a locality name that is commonly used.

‘Settlement’ attribute – based on the settlement names in Ordnance Survey’s Meridian^TM dataset, whose history is in our 1:250 000 scale gazetteer. This dataset is maintained and updated annually.

‘Local Authority’ attribute –  based on the Ordnance Survey Boundary-Line dataset derived from Boundary Commission data and is maintained and updated twice a year under a statute. 

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