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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
 
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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