> 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-mastermap-topography-layer-building-height-attribute/release-notes/october-2025.md). # October 2025 Building Height Attribute (BHA) is an enhancement to, and forms part of, OS MasterMap Topography Layer. It provides a set of height attributes with a buildings theme within OS MasterMap Topography Layer. ## Building Height Attribute tiles * **Total tiles**: 9 971 * **New tiles**: 3 \[NG0590, SW2510 and SX3530] * **Deleted tiles**: 9 \[NO4085, NR4545, NT4080, NY7520, SS1515, SX0035, TM4545, TM5595 and TR2570] ## Extent The October 2025 BHA release contains building heights for **45 393 635** unique buildings, tanks, chimneys and glasshouses across the entirety of Great Britain. The total number of features is 45 575 638, including duplicate TOIDs (these are recorded when features overlap at tile edges). ## Limitations Some building TOIDs (Topographic Identifiers) in OS MasterMap Topography Layer will have no corresponding height values in the BHA data in areas of coverage. This can occur because of different update cycles or in instances when a building was constructed after the capture of the source BHA data. This is also the case when a building has failed quality validation checks and there is no existing data to replace it. Building height values are generated from a fully automated process and, as such, the accuracy of the values is subject to tolerances governed by the process. Ordnance Survey specifically disclaims any warranty that OS MasterMap Topography Layer – BHA is of satisfactory quality or fitness for a particular purpose. We further disclaim any warranty that OS MasterMap Topography Layer – BHA is error free or accurate. ## Next release The next release of OS MasterMap Topography Layer – BHA is scheduled for **April 2026**. ## Improvements The October 2025 release includes the below improvements: * An updated **BHA\_ProcessDate** for each OS\_TOPO\_TOID. * Enhanced **height validation rules** have been introduced, resulting in two small changes that may be noticeable in the product: * Building features with a geometry area less than 8m² have been filtered out of the product. * The AbsHMax will always be greater than the AbsH2, whereas previously it could be the case that the roof edge was higher than the roof maximum. * Enhancements to the calculation and population of the **Confidence Level attribute**. This provides new, clearer definitions for each confidence level to facilitate more informed data-driven decisions. These definitions will be consistent with the height data already being published in the [OS NGD Buildings Theme](https://docs.os.uk/osngd/data-structure/buildings). --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.os.uk/os-downloads/products/buildings-and-infrastructure-portfolio/os-mastermap-topography-layer-building-height-attribute/release-notes/october-2025.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.