> 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/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-overview/feature-types-in-the-product.md). # Feature types in the product The core feature types available in OS MasterMap Water Network Layer. OS MasterMap Water Network Layer features are classified into feature types. Each feature type has associated attribution, and further detail can be found in the [OS MasterMap Water Network Layer Technical Specification](/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification.md). The product has two core feature types: **WatercourseLink** and **HydroNode**. ## WatercourseLink Feature Type A WatercourseLink feature represents the alignment of a watercourse; the majority have been derived from Ordnance Survey's detailed topographic data, made available to customers as the [OS MasterMap Topography Layer](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer.md) product. WatercourseLink features are split in the following circumstances: * Where two or more watercourses meet * Where the real-world-based attribution of a watercourse changes * Where the name of a watercourse changes or ceases to apply WatercourseLink features are not split where they pass under or over one another at different levels. They may be split where they pass into a culvert or tunnel or onto an aqueduct. Height has been added to each vertex coordinate using the raw data used to create the OS Terrain height products.

An example map showing the WatercourseLink feature which represents the alignment of watercourses. All watercourses on the map extract have a blue solid line on top of them to show their alignment - theWatercourseLink feature. — *The WatercourseLink feature represents the alignment of watercourses.*

## HydroNode Feature Type A HydroNode feature explicitly represents the source, sink or junction of a watercourse. In addition, they record the location where any real-world-related attribution changes. A HydroNode feature may only exist at the end point of a WatercourseLink feature. Height has been added to the coordinate for the HydroNode using the raw data used to create the OS Terrain height products.

An example map showing the HydroNode feature which explicitly represents the source, sink or junction of a watercourse. All watercourses on the map extract have white circles with a solid blue outline on them at various points to represent the HydroNode feature. — *The HydroNode feature explicitly represents a watercourse's source and sink, and locations where junctions of watercourses exist.*

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