March 2025

This release note provides information about the latest release of OS MasterMap (OSMM) Topography Layer, released to customers on 17 March 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 16/01/2025 (Last Release)	Count on 27/02/2025 (This Release)
Total Feature Count	511 810 856	512 632 961
Count of Topo Area	128 057 901	128 273 981
Count of Topo Line	352 786 062	353 377 395
Count of Topo Point	4 392 607	4 394 656
Count of Topo Bline	524 015	523 727
Count of Topo CartoSym	3 780 237	3 780 848
Count of Topo CartoTxt	22 270 034	22 282 354
Total Count of Deletes	765 539	814 144
Count of Topo Area deletions	159 535	175 473
Count of Topo Line deletions	587 397	616 657
Count of Topo Point deletions	1 974	2 235
Count of Topo Bline deletions	552	707
Count of Topo CartoSym deletions	2 326	3 024
Count of Topo CartoTxt deletions	13 755	16 048
Total Count of Inserts	1 344 942	1 636 249
Count of Topo Area inserts	311 910	391 553
Count of Topo Line inserts	1 004 309	1 207 990
Count of Topo Point inserts	2 856	4 284
Count of Topo Bline inserts	427	419
Count of Topo CartoSym inserts	2 410	3 635
Count of Topo CartoTxt inserts	23 030	28 368
Total Count of Modifications	1 388 390	1 640 594
Count of Topo Area Modifications	716 331	826 746
Count of Topo Line Modifications	657 686	782 736
Count of Topo Point Modifications	260	262
Count of Topo Bline Modifications	671	1 304
Count of Topo CartoSym Modifications	36	21
Count of Topo CartoTxt Modifications	13 406	29 525
COU Size (bytes)	589 321 042	675 322 893

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)
osgb5000005299253195	412771.500, 601311.887
osgb5000005263740431	422076.291, 299541.750
osgb1000000013979343	510060.446, 476948.989
osgb1000000292571752	273370.555, 873670.418
osgb5000005284097242	372550.824, 407494.624
osgb1000002006355269	5523489.470, 432425.260

Discrepancies

In this release 33 errors were detected, of which, 3 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 28 April 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).