- Category: Water Feature
- Type: Island
- Latitude/Longitude: 52°47'15"N 4°41'39"W
- Eastings/Northings: 218414, 324526
- OS Grid: SH184245
- Mapcode Local: GBR GPSB.8J0
- Mapcode Global: WH33T.V6T6
Location and coordinates are for the approximate centre of Ynys Gwylan-fawr within this administrative area.
Geographic features and populated places may cross administrative borders.