# How Field Boundary data is created
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The content on this page supplements that provided on the [Field Boundary Feature Type](https://docs.os.uk/osngd/data-structure/structures/structure-features/field-boundary) page.
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Diagram showing how Field Boundary data is created.
Field Boundary data is created by an automated process. The inputs to the process are OS NGD Structure 'Built Obstruction' Lines, OS aerial imagery (25cm), Digital Surface Model (DSM) and Digital Terrain Model (DTM).
1. After new imagery is available and the topographic area updates in 10km-by-10km areas are complete, the automated process is run to classify features and calculate height and width values.
2. Field Boundary features are coincident with and reference the underlying parent OS NGD Structures ‘Built Obstruction’ Line. Field Boundary features follow the existing geometry of the Built Obstruction line.
3. Field Boundary features may be subdivisions of the Built Obstruction line where different classifications can be identified from OS aerial imagery. Where the line is not recognised as a vegetated or wall feature, the Field Boundary feature is classified as ‘Other’ (for example, fences, or newly planted hedges where features are too small to be identified from 25cm aerial imagery). Where the classification of Field Boundary features has not yet taken place by the automated process, these features are classified as ‘Unknown’.
4. Where more than one classification is present, the classification hierarchy is used to decide which classification should be applied, that is, Tree Canopy (highest) to Unknown (lowest). Any classified section of Field Boundary feature less than 4.0metres is ignored and subsumed into the surrounding classified sections based on the hierarchy.
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