> 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/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/september-2026.md).

# September 2026

This release note provides information about the latest release of OS MasterMap (OSMM) Topography Layer, released to customers on 14 September 2026.

## OSMM Topography Layer product count

The following table contains product counts for this release of OSMM Topography Layer data. The dates shown are extraction dates, not release dates.

<table><thead><tr><th>OSMM Topography Layer</th><th width="212.39999389648438">Count on 27/08/2026 (This Release)</th><th>Count on 16/07/2026 (Last Release)</th></tr></thead><tbody><tr><td><strong>Total Feature Count</strong></td><td><strong>520 036 963</strong></td><td><strong>519 342 087</strong></td></tr><tr><td>Count of Topo Area</td><td>130 131 133</td><td>129 958 160</td></tr><tr><td>Count of Topo Line</td><td>358 640 755</td><td>358 140 859</td></tr><tr><td>Count of Topo Point</td><td>4 476 182</td><td>4 473 894</td></tr><tr><td>Count of Topo Bline</td><td>517 277</td><td>517 322</td></tr><tr><td>Count of Topo CartoSym</td><td>3 859 556</td><td>3 858 766</td></tr><tr><td>Count of Topo CartoTxt</td><td>22 412 110</td><td>22 393 086</td></tr><tr><td><strong>Total Count of Deletes</strong></td><td>829 975</td><td><strong>756 720</strong></td></tr><tr><td>Count of Topo Area deletions</td><td>160 663</td><td>143 937</td></tr><tr><td>Count of Topo Line deletions</td><td>627 683</td><td>565 880</td></tr><tr><td>Count of Topo Point deletions</td><td>3 230</td><td>2 577</td></tr><tr><td>Count of Topo Bline deletions</td><td>881</td><td>1 289</td></tr><tr><td>Count of Topo CartoSym deletions</td><td>4 286</td><td>4 306</td></tr><tr><td>Count of Topo CartoTxt deletions</td><td>33 232</td><td>38 731</td></tr><tr><td><strong>Total Count of Inserts</strong></td><td><strong>1 524 851</strong></td><td><strong>1 381 876</strong></td></tr><tr><td>Count of Topo Area inserts</td><td>333 636</td><td>301 953</td></tr><tr><td>Count of Topo Line inserts</td><td>1 127 579</td><td>1 016 881</td></tr><tr><td>Count of Topo Point inserts</td><td>5 518</td><td>3 846</td></tr><tr><td>Count of Topo Bline inserts</td><td>786</td><td>801</td></tr><tr><td>Count of Topo CartoSym inserts</td><td>5 076</td><td>4 090</td></tr><tr><td>Count of Topo CartoTxt inserts</td><td>52 256</td><td>54 305</td></tr><tr><td><strong>Total Count of Modifications</strong></td><td><strong>1 863 681</strong></td><td><strong>2 087 450</strong></td></tr><tr><td>Count of Topo Area Modifications</td><td>756 781</td><td>683 458</td></tr><tr><td>Count of Topo Line Modifications</td><td>1 083 725</td><td>1 381 302</td></tr><tr><td>Count of Topo Point Modifications</td><td>477</td><td>527</td></tr><tr><td>Count of Topo Bline Modifications</td><td>1 589</td><td>1 090</td></tr><tr><td>Count of Topo CartoSym Modifications</td><td>59</td><td>29</td></tr><tr><td>Count of Topo CartoTxt Modifications</td><td>21 050</td><td>21 044</td></tr><tr><td><strong>COU Size (bytes)</strong></td><td><strong>625 709 056</strong></td><td><strong>579 604 480</strong></td></tr></tbody></table>

## Changed TOIDs

Numerous TOIDs (Topographic Identifiers) have changed since the last refresh, resulting in a visual difference in the data. The list below shows a sample of changed TOIDs and their locations that you can use as 'lookup samples' to validate that your latest supply has updated correctly:

| TOID                 | Location (i.e. XY Coordinates) |
| -------------------- | ------------------------------ |
| osgb1000000288291787 | 270146.96, 920297.19           |
| osgb5000005221597925 | 211974.25, 321328.51           |
| osgb1000002006579810 | 525870.081, 411471.736         |
| osgb5000005221458378 | 324640.686, 869556.351         |
| osgb5000005161118396 | 288008.622, 378479.98          |
| osgb5000005358902949 | 584702.317, 169488.825         |

## Discrepancies <a href="#hlk115182660" id="hlk115182660"></a>

In this release 7 errors were detected. These are all considered to be minor errors and there are no major errors present. All previous errors have been fixed.

We aim to have all errors resolved prior to the next release as part of ongoing quality improvements.

## Next release

The next release of OS MasterMap Topography Layer is scheduled for **26** **October 2026.**


---

# 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/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/september-2026.md?ask=<question>&goal=<endgoal>
```

`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.