> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/areas-and-zones-portfolio/boundary-line/boundary-line-technical-specification/shapefile-tab-and-gkpg/features-shapefile-tab-and-gpkg/link-feature-type.md).

# Link feature type

Links represent all linear features; that is boundaries, extent of the realm (EOR) and mean high water (springs) mark (MHW). All links are broken when they intersect with one another. The first and last coordinate pairs in a link correspond exactly with the end coordinates of the adjoining link(s). Links may comprise up to several thousand line segments.

## Feature type attributes <a href="#feature-type-attributes" id="feature-type-attributes"></a>

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.

### fid

Feature identifier added by the software.

* **Attribute Name**: fid (GPKG), Not provided (TAB), Not provided (Shapefile)
* **Multiplicity**: \[0..1]

### Shape

Feature geometry.

* **Attribute Name**: Not provided (GPKG), Not provided (TAB), SHAPE (Shapefile)
* **Data Type**: Polyline
* **Multiplicity**: \[1]

### Feature code

Code value assigned to the Mean High Water Line polyline. This value will always be set to `– 0071` as this is the feature code applicable to a Mean High Water Line feature.

* **Attribute Name**: Feature\_Code (GPKG), Feature\_Code (TAB), CODE (Shapefile)
* **Data Type**: char
* **Size**: 4
* **Multiplicity**: \[1]

### Feature description

Description of the boundary feature. Set to ‘High Water Mark’ (HWM)

* **Attribute Name**: Feature\_Description (GPKG), Feature\_Description (TAB), DESCRIPT0 (Shapefile)
* **Data Type**: char
* **Size**: 21
* **Multiplicity**: \[1]

### File name

Name of the boundary polygon that the line is contained by; written in UPPERCASE with underscores.

{% hint style="info" %}
The high water mark line is split up by every boundary that it crosses. Where the resulting line is contained in multiple polygons, for the product the same geometry is used for multiple features, with the `File_Name` referencing the containing boundary polygon, and the same `Global_Link_ID` used for all of them.
{% endhint %}

* **Attribute Name**: File\_Name (GPKG), File\_Name (TAB), FILE\_NAME (Shapefile)
* **Data Type**: char
* **Size**: 100
* **Multiplicity**: \[1]

### Feature serial number

Serial number applied to the polyline feature during the production of the product.

{% hint style="info" %}
In the current product, this is not unique nor maintained.
{% endhint %}

* **Attribute Name**: Feature\_Serial\_Number (GPKG), Feature\_Serial\_Number (TAB), NUMBER (Shapefile)
* **Data Type**: Integer (TAB), Number (Shapefile)
* **Size**: n/a (TAB), 11 (Shapefile)
* **Multiplicity**: \[1]

### Global link ID

A maintained sequential integer identifier that is unique, except for records with duplicate geometry referencing multiple boundary polygons.

* **Attribute Name**: Global\_Link\_ID (GPKG), Global\_Link\_ID (TAB), LINK\_ID (Shapefile)
* **Data Type**: Integer (TAB), Number (Shapefile)
* **Size**: n/a (TAB), 11 (Shapefile)
* **Multiplicity**: \[1]


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