15 minutes of latitude and longitude in each quadrangle, using the traditional nomenclature system of degrees (°), minutes ('), and seconds (").

I love the 15' USGS topographical maps (topos). What I often do is carefully cut out the map itself, without the white margins, into four quarters, pasting them onto unbleached muslin, about 3-4 mm apart, then painting the map with some waterproofing. That way, there is no fold crease, and I don't have the topo blowing in the wind. I paste the topo quadrangle name and info from the margin on one cover. For the USGS 7½' topos, I cut them into nine pieces. I have been doing this since I was a Boy Scout.