July 2025

This release note provides information about the latest release of OS MasterMap (OSMM) Topography Layer, released to customers on 30 July 2025.

For awareness, users may notice some changes in this release (30 July 2025) which have been outlined below. These issues have been present in some customer supplies of the GML format between 28 June 2025 and Friday 01 August.

If the changes have impacted you and you would like a resupply, please contact us via the website or email us at [e-mail].

Broken download links for OS MasterMap Topography Layer GML 5km² tile download orders

Customer Topography 5km² tile download orders in GML format, supplied from 30 July 2025 to 12 August 2025 contain broken download links. As a result, an error message will be displayed saying there is no data available to download.

This issue was fixed on 12 August 2025 and new orders after this date will not be affected. Any customers impacted by this issue will be contacted directly. We aim to resupply all orders by 15 August 2025.

Where customers have placed an initial one off order, we advise reordering the data or contacting our fulfilment team (email us at [e-mail]) to request a resupply. We apologise for any inconvenience this has caused.

Issues affecting Geographically Chunked GML supply

Issue 1: osgb:BoundedBy Tag

BoundedBy is the minimum bounding rectangle (MBR) that encloses all features actually returned in the dataset, not just the area requested. It provides metadata about the spatial extent of the returned data, which may be smaller or larger than the queryExtent, depending on what features exist in the dataset. For example, if your queryExtent includes a large area but only a few features are returned in a small corner, the boundedBy will reflect just that smaller area.

This metadata tag was found to be missing in some GeoChunk GML files in this release of OS MasterMap Topography Layer.

Issue 2: standalone=’yes’

This is usually found in the opening line of all geographically chunked GML files for OS MasterMap Topography Layer, but is missing from this release for some orders.

The tag of standalone=’yes’ means the GML does not rely on any external DTD (Document Type Definition). All the information needed to parse and validate the GML is contained within the file itself.

Issues affecting Non-Geographically Chunked GML COU (change only update) supply

Issue 3: 'queryChangeSinceDate' tag

This tag is usually published in OSMM Topography Layer COU to inform users of when the changes apply from, but it is missing from some customer data supplies in this release of the GML file. It can be used as part of the COU load process.

The fix for this issue has been implemented and is being thoroughly tested before being deployed to our live systems. Once testing has passed the distribution of customer orders for non-geographically chunking product variation orders will be resumed.

Future releases of OS MasterMap Topography Layer

For this release, the publication date was 30 July 2025 and the extraction date was 10 July 2025.

There will be no impact on future release cycles. The next release date for OS MasterMap Topography Layer will be 01 September 2025 as scheduled on our product refresh dates page, with an extraction date of 14 August 2025.

Extraction date refers to the specific day on which data is retrieved from the database to initiate its transformation into product format. All updates made to the data up to approximately midnight preceding the extraction date are included. For instance, if the extraction date is 10 July 2025, it encompasses changes made until around midnight on 09 July 2025.

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.

OSMM Topography Layer	Count on 22/05/2025 (Last Release)	Count on 09/07/2025 (This Release)
Total Feature Count	514 001 673	514 588 789
Count of Topo Area	128 614 896	128 761 716
Count of Topo Line	354 331 329	354 746 696
Count of Topo Point	4 424 319	4 433 437
Count of Topo Bline	523 292	523 308
Count of Topo CartoSym	3 811 266	3 822 237
Count of Topo CartoTxt	22 296 571	22 301 395
Total Count of Deletes	390 811	400 830
Count of Topo Area deletions	85 937	84 645
Count of Topo Line deletions	285 889	289 224
Count of Topo Point deletions	3 240	4 199
Count of Topo Bline deletions	280	366
Count of Topo CartoSym deletions	3 869	1 762
Count of Topo CartoTxt deletions	11 596	18 573
Total Count of Inserts	1 059 781	987 946
Count of Topo Area inserts	250 612	231 465
Count of Topo Line inserts	749 761	704 591
Count of Topo Point inserts	18 904	13 317
Count of Topo Bline inserts	176	382
Count of Topo CartoSym inserts	20 444	14 803
Count of Topo CartoTxt inserts	19 884	23 397
Total Count of Modifications	849 996	786 151
Count of Topo Area Modifications	403 456	372 940
Count of Topo Line Modifications	433 798	396 665
Count of Topo Point Modifications	857	1 046
Count of Topo Bline Modifications	883	1 997
Count of Topo CartoSym Modifications	37	86
Count of Topo CartoTxt Modifications	10 965	13 429
COU Size (bytes)	416 198 799	388 693 359

CartoSym counts were added to this release note on 07 August 2025. All other counts including total counts and COU size have not changed since initial publication.

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)
osgb5000005298892943	123804.745, 860066.192
osgb5000005255435016	331562.51, 496930.79
osgb1000000013752053	508667.053, 431390.732
osgb5000005336494913	310555.05, 968584.1
osgb1000000083528931	470646.99, 465628.53
osgb1000002503340685	532497.94, 406843.42

Discrepancies

In this release, 356 errors were detected, of which 99 are new errors. These are all considered to be minor errors. There are no known major errors present.

This spike in error counts has been investigated, and the cause found to be 'slitheres' between polygons and extra vertices where lines intersect. These will not be visible in product, and should not impact the customer.

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 01 September 2025.

Land cover refinement changes

The land cover specification for rural geographies has been refined. The Mountain and Moorland refinement was completed in 2022.

The rural geography updates began capture in May 2022. The initial updates fed through to the July 2022 release of OSMM Topography Layer, with the multi class land cover polygons completed in December 2022. The single class land cover polygons will continue to feed through to product from April 2023.

The following two tables articulate this specification refinement:

Old land cover specification

Geographic Area	Minimum Area Size for Land Cover	Minimum Width
Urban	0.1hectares (ha) (1 000m²)	5m
Rural	0.1hectares (ha) (1 000m²)	10m
Mountain and moorland	1.0hectares (ha) (10 000m²)	10m

New land cover specification

Geographic Area	Minimum Area Size for Land Cover	Minimum Width
Urban	0.1hectares (ha) (1 000m²)	5m
Rural	0.1hectares (ha) (1 000m²)	5m*
Mountain and moorland	0.1hectares (ha) (1 000m²)*	5m*

The asterisk symbol (*) shows which criteria have been refined.

The land cover specification refinement means that the rural land cover data within OSMM Topography Layer will become more granular, producing a more detailed view made up of smaller more numerous polygons. This provides users with more accurate data that meets each individual’s specific requirements. These changes are purely refinements and do not change the data attribution.

Annex A shows three examples of how the rural land cover refinement is being translated into OSMM Topography Layer.

Annex A: Rural land cover specification refinement examples

Below are three real-world examples of how the rural land cover specification refinement has affected the data within OSMM Topography Layer. The examples showcase three areas in southern Scotland where the specification refinement has broken up one land polygon within the Topographic Area Feature Type into smaller, separate polygons.

Example one

Location of example area one:

5km Tile	OS Grid Reference	Coordinates (OSGB36)
NS4505	NS 47825 05240	247790.7, 605224.0

TOIDs for example area one:

• OSMM Topography Layer (July 2022): osgb1000000316775097

• OSMM Topography Layer (August 2022): osgb5000005297485451, osgb5000005297485455, osgb5000005297485456

Source imagery of example area one for comparative purposes:

Photo of imagery of an area in southern Scotland taken in January 2021 highlighting an area of rural land cover. Provided for comparative purposes to show how the rural land cover specification refinement has altered the data in example area 1.

Data before the rural land cover specification refinement update (OSMM Topography Layer – July 2022):

Screenshot of what the data in example area 1 looked like prior to the rural land cover specification refinement update (July 2022 OS MasterMap Topography Layer data).

Data after the rural land cover specification refinement update (OSMM Topography Layer – August 2022):

Screenshot of what the data in example area 1 looked like after the rural land cover specification refinement update (August 2022 OS MasterMap Topography Layer data).

Example two

Location of example area two:

5km Tile	OS Grid Reference	Coordinates (OSGB36)
NX3540	NX 37464 41871	237419, 541979

TOIDs for example area two:

• OSMM Topography Layer (July 2022): osgb1000000318639911

• OSMM Topography Layer (August 2022): osgb1000000318639911, osgb5000005298080383, osgb5000005298080465

Source imagery of example area two for comparative purposes:

Photo of imagery of an area in southern Scotland highlighting an area of rural land cover. Provided for comparative purposes to show how the rural land cover specification refinement has altered the data in example area 2.

Data before the rural land cover specification refinement update (OSMM Topography Layer – August 2022):

Screenshot of what the data in example area 2 looked like prior to the rural land cover specification refinement update (August 2022 OS MasterMap Topography Layer data).

Data after the rural land cover specification refinement update (OSMM Topography Layer – October 2022):

Screenshot of what the data in example area 2 looked like after the rural land cover specification refinement update (October 2022 OS MasterMap Topography Layer data).

Example three

Location of example area three:

5km Tile	OS Grid Reference	Coordinates (OSGB36)
NX6550	NX 68975 51146	268968, 551139

TOIDs for example area three:

• OSMM Topography Layer (July 2022): osgb1000000319079420

• OSMM Topography Layer (August 2022): osgb1000000319079420, osgb5000005298106224

Source imagery of example area three for comparative purposes:

Photo of imagery of an area in southern Scotland highlighting an area of rural land cover. Provided for comparative purposes to show how the rural land cover specification refinement has altered the data in example area 3.

Data before the rural land cover specification refinement update (OSMM Topography Layer – August 2022):

Screenshot of what the data in example area 3 looked like prior to the rural land cover specification refinement update (August 2022 OS MasterMap Topography Layer data).

Data after the rural land cover specification refinement update (OSMM Topography Layer – October 2022):

Screenshot of what the data in example area 3 looked like after the rural land cover specification refinement update (October 2022 OS MasterMap Topography Layer data).