NRS HydroLock Mapcessory Map Case Four sizes to accommodate most maps, charts or books, as well as essentials such as wallets, snacks and a warm hat Interior window dimensions (L x W): XS (6" x 9"), S (8" x 12"), M (15" x 12"), L (18" x 15") Overall dimensions (L x W): XS (10" x 11"), S (12" x 14"), M (19" x 14"), L (22" x 17") The HydroLock zip seal provides a totally waterproof closure, a clear urethane window lets you see both sides of your map, chart or guide Attachment points in the corners make the NRS HydroLock Map Case easy to lash to your boat or a deck bag so it's always right there when you need it