----------------------------Original message---------------------------- What are the rules about the physical dimensions of USGS 7-1/2 minute quads? They're all 27' long; most of the USA seems to have quads 22" wide, but some at lower latitudes are 23" wide and some in Florida and South Texas are 24" wide. Are there any specific cut-off latitudes that form a boundary between sheets of different widths (wider below that lat and narrower above)? Are the wide ones limited only to certain states? Unfortunately, I've noticed that at exactly the same latitude in S. Texas are quads of both 23" and 24" in width, so I suspect there isn't a nice cut-and-dry answer. I guess USGS policy has changed over the years. But I'd appreciate whatever anyone knows about this. Thanks ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Mark Thomas | The train ... traditional, Evans Library, Texas A&M University | yet environmentally sound (409) 862-1052 / FAX (409) 845-6238 | [log in to unmask] | --Lisa Simpson