July 2025
This release note provides information about the latest release of OS MasterMap (OSMM) Topography Layer, released to customers on 30 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.
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 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 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 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 CartoTxt Modifications
10 965
13 429
COU Size (bytes)
416 198 799
388 693 359
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:
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
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
Urban
0.1hectares (ha) (1 000m²)
5m
Rural
0.1hectares (ha) (1 000m²)
5m*
Mountain and moorland
0.1hectares (ha) (1 000m²)*
5m*
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:
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:
Data before the rural land cover specification refinement update (OSMM Topography Layer – July 2022):
Data after the rural land cover specification refinement update (OSMM Topography Layer – August 2022):
Example two
Location of example area two:
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:
Data before the rural land cover specification refinement update (OSMM Topography Layer – August 2022):
Data after the rural land cover specification refinement update (OSMM Topography Layer – October 2022):
Example three
Location of example area three:
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:
Data before the rural land cover specification refinement update (OSMM Topography Layer – August 2022):
Data after the rural land cover specification refinement update (OSMM Topography Layer – October 2022):
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