> For the complete documentation index, see [llms.txt](https://docs.os.uk/osngd/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/osngd/code-lists/code-lists-overview/boundaryhighwatermarkdescriptionvalue.md).

# boundaryhighwatermarkdescriptionvalue

This code list is used in association with the Description attribute which is present within the Boundary High Water Mark Feature Type. The code list marks the features as a high water mark to make selection and filtering of features easier when used with other data.

| Label                    | Definition                                                                                                                                                                                                                                                                                                                                                                                |
| ------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Boundary High Water Mark | A generalised version of the detailed scale high water mark data that’s available in the Tidal Boundary and Tidal Boundary Continuous High Feature Types within the OS NGD Water Theme. In England and Wales this is the average alignment of the high tides halfway between spring and neap tides, and in Scotland this is the average alignment of the high tides only at spring tides. |


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