Boundary High Water Mark
In the OS NGD Boundaries Collection, the mean high water (springs) mark is shown to the normal tidal limit (NTL). Areas of salt marsh, mudflats and so on often have extremely complicated tide lines. For ease of digitising and to reduce data volumes, mean high water may be generalised in these areas (not Scotland). The mean high water (springs) mark is represented in the OS NGD Boundaries Collection by a polyline feature. The mean high water (springs) mark is subject to continuous change, but the captured alignment of a tide line is a snapshot on one day. It is not practical to revise tide lines frequently.
Temporal filtering
The earliest date on which you can request a one-off snapshot of a date in the past for data in this feature type is 29 September 2022.
Feature type attributes
The following sub-sections provide details about the attributes included with this feature type, their data types in the different output formats, and other important metadata about them.
osid
Primary identifier for the feature. The OSID is a Globally Unique Identifier (GUID) and requires no centralised authority to ensure uniqueness. Note that the same OSID can occur in more than one feature type when a single feature is represented multiple times in the OS NGD.
Data Types: String (GPKG), String (CSV)
Nullable: false
Max Length: 36
OS Select+Build Filterable: No
Data Schema Version: 1.0
versiondate
Date when the version was last updated.
Data Types: Date (GPKG), Date (CSV)
Nullable: false
OS Select+Build Filterable: No
Data Schema Version: 1.0
versionavailablefromdate
The date this version of the feature became the latest version.
Data Types: DateTime (GPKG), DateTime (CSV)
Nullable: false
OS Select+Build Filterable: No
Data Schema Version: 1.0
versionavailabletodate
The date this version of the feature was superseded by an update or ceased to exist.
Data Types: DateTime (GPKG), DateTime (CSV)
Nullable: true
OS Select+Build Filterable: No
Data Schema Version: 1.0
changetype
The type of change that generated a new version of the feature.
Data Types: String (GPKG), String (CSV)
Nullable: false
Code List Name: changetypevalue
Max Length: 50
OS Select+Build Filterable: No
Data Schema Version: 1.0
geometry
Geometry for the feature.
Data Types: Geometry (GPKG), WKT (CSV)
Nullable: false
OS Select+Build Filterable: No
Data Schema Version: 1.0
Geometry Type: LineString
geometry_length
The measured length of the geometry in metres.
Data Types: Float (GPKG), Real (CSV)
Nullable: false
Precision: 18
Scale: 6
OS Select+Build Filterable: No
Data Schema Version: 1.0
theme
The OS NGD theme to which this feature belongs.
Data Types: String (GPKG), String (CSV)
Nullable: false
Code List Name: themevalue
Max Length: 40
OS Select+Build Filterable: No
Data Schema Version: 1.0
description
A single descriptive value intended for a quick understanding of what the feature represents.
Data Types: String (GPKG), String (CSV)
Nullable: false
Code List Name: boundaryhighwatermarkdescriptionvalue
Max Length: 50
OS Select+Build Filterable: Yes
Data Schema Version: 1.0
boundarytype
A single description value for boundary type.
Data Types: String (GPKG), String (CSV)
Nullable: false
Code List Name: boundarytypevalue
Max Length: 50
OS Select+Build Filterable: Yes
Data Schema Version: 1.0
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