> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/buildings-and-infrastructure-portfolio/os-open-linked-identifiers/os-open-linked-identifiers-technical-specification/blpu_uprn_topographicarea_toid_5.md).
# BLPU\_UPRN\_TopographicArea\_TOID\_5
This page aims to provide all the information to evaluate if the method of associating the respective identifiers is suitable for your needs. These identifier relationships have been extracted from existing premium products and are presented in a standalone table for easy and open access to the information. It describes which product the information was extracted from, what information was extracted and how the source product derived the original association between the identifiers.
Topographic area identifier showing AddreessBase Premium and MasterMap Topography layer data combined
## Relationship Extraction
The relationship between the Unique Property Reference Number (UPRN) of *AddressBase Premium* and the Topographic Identifier (TOID) of the TopographicArea feature in the *OS MasterMap Topography Layer* product is extracted for all live, provisional and historic BLPU records in *AddressBase Premium*.
Data from the *OS MasterMap Topography Layer* TopographicArea feature and *AddressBase Premium BLPU* table are joined where the TOID equals the CROSS\_REFERENCE of the AddressBase Premium Cross- Reference table and the source is equal to ‘7666MT’.
The relationship is extracted from *AddressBase Premium* after the release of each six weekly Epoch. Further information on the relationship extraction, including the date of extraction and product version information, are provided in the Product Version Information File.
## Correlation Method
The relationship is determined by a point in a polygon intersection between the Address seed location and the TopographicArea polygon. The relationship is performed by [GeoPlace,](https://www.geoplace.co.uk/) a joint venture between Ordnance Survey and Local Government Association (LGA) who produce *AddressBase*.
*AddressBase Premium* and *OS MasterMap Topography Layer* are updated every six weeks but on different release cycles. Therefore, some of the version information in the product may have changed and mean that the relationship is out of sync.
A Confidence Value is assigned to indicate the reliability of the version information provided in this product in relation to the version of the features used to form the correlation in the original product. The Confidence Value is given for each relationship, which is defined in this relationship as:
| Confidence Value | Definition |
| ------------------------------------------- | ------------------------------------------------------------------------------------------------------------------- |
| Version information is correct | The version information provided is the same as the version of the feature used to create the correlation. |
| Version information has potentially changed | The version information could be different from the version of the feature that was used to create the correlation. |
| Version information has changed | The version information provided is different from the version of the feature used to create the correlation. |
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