# March 2026

## OSMM Topography Layer product count

{% hint style="info" %}

### Increase in Change-Only Updates

Some customers may see an increase in Change-Only Updates (COU). This is as a result of improvements being made to the accuracy of position attributes rather than the addition of new physical features. These updates have been rolled out for Scotland, with similar updates for England and Wales to follow in future releases.

For more information on this recent update see the [Product Announcements page](/os-downloads/resources/product-resources/product-announcements.md#march-2026-update-to-os-mastermap-topography-layer-to-improve-the-accuracy-of-position-attributes).
{% endhint %}

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 valign="bottom">OS MM Topography Layer</th><th valign="middle">Count on 29/01/2026 (Last Release)</th><th valign="middle">Count on 12/03/2026 (This Release)</th></tr></thead><tbody><tr><td valign="bottom"><strong>Total Feature Count</strong> </td><td valign="middle"><strong>517 279 866</strong> </td><td valign="middle"><strong>517 764 300</strong></td></tr><tr><td valign="bottom">Count of Topo Area              </td><td valign="middle">129 436 199 </td><td valign="middle">129 557 449 </td></tr><tr><td valign="bottom">Count of Topo Line              </td><td valign="middle">356 666 805 </td><td valign="middle">357 013 181 </td></tr><tr><td valign="bottom">Count of Topo Point             </td><td valign="middle">4 469 251 </td><td valign="middle">4 471 108 </td></tr><tr><td valign="bottom">Count of Topo Bline             </td><td valign="middle">520 431 </td><td valign="middle">520 000 </td></tr><tr><td valign="bottom">Count of Topo CartoSym          </td><td valign="middle">3 859 805 </td><td valign="middle">3 860 384 </td></tr><tr><td valign="bottom">Count of Topo CartoTxt          </td><td valign="middle">22 327 375 </td><td valign="middle">22 342 178 </td></tr><tr><td valign="bottom"><strong>Total Count of Deletes</strong>       </td><td valign="middle"><strong>678 764</strong> </td><td valign="middle"><strong>603 688</strong></td></tr><tr><td valign="bottom">Count of Topo Area deletions       </td><td valign="middle">134 834 </td><td valign="middle">121 842 </td></tr><tr><td valign="bottom">Count of Topo Line deletions       </td><td valign="middle">492 827 </td><td valign="middle">451 542 </td></tr><tr><td valign="bottom">Count of Topo Point deletions      </td><td valign="middle">3 157 </td><td valign="middle">2 088 </td></tr><tr><td valign="bottom">Count of Topo Bline deletions      </td><td valign="middle">527 </td><td valign="middle">710 </td></tr><tr><td valign="bottom">Count of Topo CartoSym deletions </td><td valign="middle">2 983 </td><td valign="middle">2 128 </td></tr><tr><td valign="bottom">Count of Topo CartoTxt deletions </td><td valign="middle">44 436 </td><td valign="middle">25 378 </td></tr><tr><td valign="bottom"><strong>Total Count of Inserts</strong>       </td><td valign="middle"><strong>1 227 441</strong> </td><td valign="middle"><strong>1 621 570</strong></td></tr><tr><td valign="bottom">Count of Topo Area inserts         </td><td valign="middle">271 858 </td><td valign="middle">776 481 </td></tr><tr><td valign="bottom">Count of Topo Line inserts         </td><td valign="middle">885 796 </td><td valign="middle">797 918 </td></tr><tr><td valign="bottom">Count of Topo Point inserts        </td><td valign="middle">6 024 </td><td valign="middle">3 945 </td></tr><tr><td valign="bottom">Count of Topo Bline inserts        </td><td valign="middle">356 </td><td valign="middle">279 </td></tr><tr><td valign="bottom">Count of Topo CartoSym inserts   </td><td valign="middle">3 413 </td><td valign="middle">2 766 </td></tr><tr><td valign="bottom">Count of Topo CartoTxt inserts   </td><td valign="middle">59 994 </td><td valign="middle">40 181 </td></tr><tr><td valign="bottom"><strong>Total Count of Modifications</strong>  </td><td valign="middle"><strong>1 158 022</strong> </td><td valign="middle"><strong>3 488 611</strong></td></tr><tr><td valign="bottom">Count of Topo Area Modifications       </td><td valign="middle">590 892 </td><td valign="middle">533 389 </td></tr><tr><td valign="bottom">Count of Topo Line Modifications       </td><td valign="middle">549 034 </td><td valign="middle">2 937 973 </td></tr><tr><td valign="bottom">Count of Topo Point Modifications      </td><td valign="middle">402 </td><td valign="middle">650 </td></tr><tr><td valign="bottom">Count of Topo Bline Modifications      </td><td valign="middle">611 </td><td valign="middle">677 </td></tr><tr><td valign="bottom">Count of Topo CartoSym Modifications </td><td valign="middle">32 </td><td valign="middle">59 </td></tr><tr><td valign="bottom">Count of Topo CartoTxt Modifications </td><td valign="middle">17 051 </td><td valign="middle">15 863 </td></tr><tr><td valign="bottom"><strong>COU Size (bytes)</strong> </td><td valign="middle"><strong>514 400 256</strong> </td><td valign="middle"><strong>538 158 030</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) |
| -------------------- | ------------------------------ |
| osgb5000005332319812 | 304055.7, 713415.97            |
| osgb1000002102502990 | 334462.68, 407435.3            |
| osgb5000005210518090 | 552998.95, 186435.15           |
| osgb1000000384343140 | 141793.136, 851689.296         |
| osgb5000005305465954 | 411421.086, 427814.947         |
| osgb5000005192059097 | 559706.5, 98008.19             |

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

In this release 32 errors were detected, of which, 10 have existed since the previous refresh. These are all considered to be minor errors and there are no major errors present.

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 **11 May 2026**.


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