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.

Any data temporally filtered earlier than the specified earliest date noted above for the data schema version may contain data inconsistencies.

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.

Loading OS NGD CSV files into databases

Comma-separated values (CSV) file format is universally supported for easy ingestion into all major database products. Before loading OS NGD data contained in CSV files into a database, it is necessary to create relevant tables. Data definition language (DDL) statements for PostgreSQL, SQL Server and Oracle can be accessed in our OS NGD Resources GitHub repository.

For instructions on loading CSV files, see the Getting Started with CSV guide.

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