THIS IS A SERIES OF BLANK MAP GRIDS THAT ARE SCALED TO EACH 5 DEGREES OF LATITUDE YOU CHOOSE THE ONE THAT IS CLOSEST TO YOUR LATITUDE AND YOUR DATA CAN BE CHARTED TO A RELATIVELY ACCURATE SCALE IT IS WATERPROOF AND DURABLE YOU CAN WRITE ON IT WITH A NUMBER OF MARKING IMPLEMENTS I.E. BALL POINT PENS, FELT TIP PENS, PENCILS, ETC IT IS DESIGNED FOR THE EASE OF CHARTING DATA FROM A GPS OR SIMILAR DEVISE IT IS USED IN RECORDING LAKE DEPTH, HIKING TRAILS, PROPERTY BOUNDARIES, ETC