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Usually the sea or ocean area.
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The High Water Mark digital dataset is derived from relevant 6 inch and 25 inch Ordnance Maps. The alterations are in accordance with the Boundary Survey Acts Ireland, approved by the Chief Boundary Surveyor and signed off in Privy Council Orders. The dataset also includes...
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Area ≥ 0.4 km² for islands in seawater. Smaller islands in inland water area can be portrayed if considered as landmark
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Start and end points of watercourses as well as confluences (Confluence, Source, Mouth, Boundary)