> 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/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/feature-types.md).

# Feature types

Two feature types are available in the OS Open Rivers product:

* [WatercourseLink](/os-downloads/products/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/feature-types/watercourselink.md)
* [HydroNode](/os-downloads/products/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/feature-types/hydronode.md)

The attributes associated with each feature type are listed on the individual feature type pages.

## Feature type attribute information

The following information will be provided against each attribute.

### Name and Definition

The name of the attribute and what it is describing.

{% hint style="info" %}

### Attribute naming across formats

Attribute names will vary slightly depending on what format you receive your data in (GML, Esri shapefile, GeoPackage or vector tiles). The attribute names on the feature type pages are written as they will appear in GML format. Attribute name mapping tables between GML and the other three formats for each feature type are present in the following pages:

* [Esri shapefile overview](/os-downloads/products/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/esri-shapefile-overview.md)
* [GeoPackage overview](/os-downloads/products/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/geopackage-overview.md)
* [Vector tiles overview](/os-downloads/products/water-portfolio/os-open-rivers/os-open-rivers-technical-specification/vector-tiles-overview.md)
  {% endhint %}

### Attribute type

The nature of the attribute, for example, a numeric value or a logical indicator.

### **Multiplicity**

Describes how many times this element is expected to be populated in the data. An attribute may be optional or mandatory within the product. These are denoted by:

* ‘1’ – There must be a value.
* ‘2’ – There must be two values.
* ‘n’ – There may be one or more values.
* ‘0’ – Population is optional.

These values may be used in combination.

### Association

An association identifies the relationship between features. These relationships are by reference only and the value will be the identifier of the referenced feature.


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