For the 24000:1 USGS DRG topo maps, the correct settings are almost always
2000 fpi & 250 dpi.
The revised standard allows for scan resolutions up to 1000 dpi, but all I
have seen are still 250.
On Sat, Feb 21, 2009 at 8:47 PM, Lee Hoffman <lhoffman(a)acm.org> wrote:
David Martin wrote:
>Your problem is the 72dpi setting. For some reason USGS topo maps do not
>"report" pixels per inch. Photoshop defaults to 72dpi, so this is what it
>tells you when that information is not present in an image.
>Your map was most likely scanned at 250dpi, per the USGS Revised DRG
Regardless of the Dots/inch setting, the Feet/inch setting must match
it. So you could have a DPI setting that is low resulting in a
somewhat higher FPI. Dave Bird used settings of 483 FPI and 72
DPI. Personally I had to use 481 FPI and 72 DPI to get a mile to be
accurate. But I could also use settings of 650 FPI and 100 DPI to
get the same results.
Hope this helps -
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