[mapserver-users] What does scale mean?

[Ed McNierney]

Steve -

The missing link is RESOLUTION, which by default is 72 DPI but which can
be changed in the MAP file.

MapServer presumes that the output device displays images at RESOLUTION
dots per inch.  This is a reasonable if someone outdated assumption for
display devices (just about all of them are higher res now).  So if 72
dots equals one inch, then a SCALE of 10,000, for example, means that 72
dots on the display equals 10,000 inches on the map, or 1" (map) =
10,000" (ground) = 72 pixels (screen).  If the screen is not exactly 72
dpi, and it's pretty much guaranteed not to be, this is only an
approximation.

That's why scale bars are very handy.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242


-----Original Message-----
From: Stephen Woodbridge [mailto:woodbri at swoodbridge.com]
Sent: Thursday, March 07, 2002 7:07 PM
To: MapServer List
Subject: [mapserver-users] What does scale mean?


OK, this may seem like a dumb question, but it occurs to me that I don't
think I know what scale means in MapServer context.

For example, if I am displaying a map file with units METERS and my
Scale is 1:1000 how are SCALE, UNITS, PIXELs related? What if my units
are DD?

TIA,
  -Steve