These pages contain specific advice about the OS NGD land cover enhancements which implement habitat mapping and percentage coverage values.

The Habitat Coverage cross reference table provides the new attribution for habitat mapping and percentage coverage by linking to the OSID. There is a one-to-many relationship which should be considered when joining the cross reference table to features in GIS software packages.

The naming of the Habitat Coverage Reference file depends on which topographic area feature it applies to, i.e.:

• OS NGD Land feature type = land_habcovref

• OS NGD Rail feature type = rail_habcovref

• OS NGD Road Track or Path feature type = roadtrackorpath_habcovref

• OS NGD Structure feature type = structure_habcovref

• OS NGD Water feature type = water_habcovref

The Habitat Coverage Reference table is included with the GeoPackage file and is available separately if data is requested in CSV format.

Natural topographic area features are mapped to:

• EUNIS habitat type hierarchical view (marine version 2022 & terrestrial version 2021) using Level 1 and Level 2 classification; and

• UK BAP Broad Habitats classification 2008

A simple algorithm automatically maps the OS Land Cover Tier B attribute of natural topographic area features to EUNIS and UK BAP classification scheme values using a lookup table prior to product publication. These are output into the Habitat Coverage Reference table.

Mapping the OS land cover classification to EUNIS Level 1 is mandatory. For EUNIS Level 2 and UK BAP it is not always possible to achieve a direct mapping as habitat classifications can be species-based, making it difficult to derive from a land cover classification. In such instances, there will be no entry for these records in the Habitat Coverage Reference table.

Coastal features also receive a habitat mapping. Coastal features are defined as being within the intertidal zone +200 metre buffer above the Mean High Water (Springs) Line.

Manual land cover classification is subjective and in the natural environment, features change over time, for example scrub becomes trees. OS carries out a flying programme each year, capturing each area of Great Britain at least once every 3 years. The aerial imagery derived from this capture programme can be impacted by seasonal variances, i.e. the time of year when the area was flown over, or even the time of day. Earlier in the year vegetated features may be captured with leaf-off, long shadows may impact the feature’s classification, or during a dry summer an area of marsh may look like rough grassland.

Additionally, the automated machine learning classification to derive the percentage cover value uses aerial imagery as a top-down view so some features on the ground may have their true nature obscured by overhanging trees.​

The automated classification of some feature types is of lower confidence and therefore the percentage cover value for these features may be of lower quality, i.e. ‘Saltmarsh’, ‘Heath’, ‘Rough Grassland’.

The land cover enhancements align the OS land cover classifications to European Nature Information System (EUNIS) and UK Biodiversity Action Plan (BAP) Broad Habitats classification scheme values and provide a percentage of each land cover classification. These enhancements apply to ‘natural’ topographic area features which exist across several OS NGD themes:

The feature’s OS Land Cover Tier B attribute is mapped to EUNIS and UK BAP Broad Habitats classification scheme values where the topographic area feature is ‘natural’, i.e. the OS Land Cover Tier A attribute is one of ‘Excavated or Deposited’, ‘Open Vegetation’, ‘Mineral’, ‘Multiple’, ‘Trees’, ‘Under Construction’ or ‘Water’.

A percentage cover value is also assigned to the OS Land Cover Tier B attribute for those features above the Mean High Water (Springs) line. Water features are not given a percentage cover value.

The land cover enhancements are supplied in a new cross-reference table. See the Habitat Coverage Reference table relating to the Land Feature Type.

The image below provides examples of these natural land cover features in the OS NGD.

Natural topographic area features above Mean High Water (Springs) are assigned a percentage value for each OS land cover classification. Water features are currently excluded from scope as it’s not always possible to confidently discern a percentage value of any additional land cover classes in the water feature using aerial imagery.

Percentage cover values are calculated against the OS Land Cover Tier B attribute by an automated machine learning process using:

• Automated interpretation of OS RGBI (25cm) aerial imagery to classify the type of land cover.

• Automated comparison against the existing OS land cover classification derived from existing capture methods.

• Automated calculation of percentage values for each OS Land Cover Tier B classification. Note: there can be up to five classifications within a single topographic area feature.

• OS Land Cover Tier B percentage values are assigned to EUNIS and UK BAP Broad Habitats classifications, where a direct mapping exists.

The percentage values are output into the Habitat Coverage Reference cross-reference table.

Example 1: Single Class Topographic Area

1. Single class topographic area feature containing ‘Non-Coniferous Trees’.

2. Cross reference table is supplied as it’s ‘Open Vegetation’.

3. OS Land Cover Tier B classification is mapped to EUNIS Level 1 and Level 2 (where possible).

4. OS Land Cover Tier B classification is mapped to UK BAP.

5. OS Land Cover Tier B classification is assigned a percentage cover of 100% by default.

6. The percentage cover value is assigned to EUNIS and UK BAP.

Example 2: Multi-Class Topographic Area

1. Multi-class topographic area feature containing ‘Rough Grassland’, ‘Scrub’, ‘Scattered Non-Coniferous Trees’.

2. Cross reference table is supplied as it’s ‘Open Vegetation’ and ‘Trees’.

3. Each OS Land Cover Tier B classification is mapped to EUNIS Level 1 and Level 2 (where possible).

4. Each OS Land Cover Tier B classification is mapped to UK BAP.

5. Each OS Land Cover Tier B classification is assigned a percentage cover value.

6. The percentage cover values are assigned to EUNIS and UK BAP.

7. OS Land Cover Tier B percentage values total 100% for an individual topographic area feature.

8. Defined OS Land Cover Tier B classifications are assigned a minimum value of 10%

Further percentage cover information

1. Percentage values are only calculated against the OS Land Cover Tier B value and then applied to EUNIS and UK BAP, where possible.

2. It's not always possible to map directly between OS Land Cover Tier B classification & EUNIS Level 2 or UK BAP so in these instances, no percentage cover value is supplied in the table.

3. Where it has not been possible to match the machine learning classification to the existing OS land cover classification, an 'Other' classification is added to the table to allow percentage values to total 100%. This can occur where features on the ground are obscured by overhanging trees. See Known Limitations for further information.

4. An 'Other' classification can have a minimum value of 5%.

5. Percentage values are rounded up in increments of 5%.

6. Percentage values can be null where a real-world change has occurred causing the topographic area feature to be updated. The percentage values for this topographic area feature will be recalculated when the automated process is next run against the updated aerial imagery.

7. Only topographic area features above Mean High Water (Springs) Line are assigned a percentage cover value. ‘Water’ topographic area features are also excluded from scope.

[1] No percentage value for Water features.

[2] Other features are included in scope where they have a natural land cover, i.e.  areas under construction are included because they are generally sand or bare earth until construction is complete. ‘Constructed’ or ‘Made’ features are out of scope.

[3] Only features above the Mean High Water (Springs) line have a percentage value.