Percentage coverage

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

Example 1 map showing Single Class Topographic Area and Habitat Coverage Reference Table

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

Example 2 map showing Multi-Class Topographic Area

Example 2 Multi-Class Topographic Area Habitat Coverage Reference Table

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.