minscale/maxscale values

[Ed McNierney]

Matt -

I will add to Steve's accurate information that the resulting scale
ratio is the scale ratio that would be produced if the output raster
image were printed or displayed at 72 dots per inch (DPI).  The
RESOLUTION statement in the map file can be used to change this number
from 72 to another value, but that only provides computational
convenience.

If you have a MAXSCALE 24000 statement, that means that at 72 DPI one
inch on the map equals 24,000 inches on the ground.  Since that's 24,000
inches over 72 dots (pixels), that's a resolution of 24,000/72 = 333.333
inches per pixel.  At 39.37 inches per meter, that is the same as 8.467
meters per pixel.

Using the default 72 DPI resolution, a MAXSCALE of 2834.64 equals
exactly one meter per pixel.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: +1 (978) 251-4242
Fax: +1 (978) 251-1396
ed at topozone.com

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Steve Lime
Sent: Wednesday, November 29, 2006 5:41 PM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: Re: [UMN_MAPSERVER-USERS] minscale/maxscale values

Matt: They are unitless values and they represent the denominator
portion of a representative fraction. So:

  MAXSCALE 24000

refers to a scale 1:24,000 and so on. It's a tad backwards (e.g. 100000
> 24000, but 1/100,000 < 1/24,000) as I'm reminded every once and a
while, but you get used to it quickly.

Steve

>>> Matthew Ganz <matt.ganz at GMAIL.COM> 11/29/2006 4:08:49 PM >>>
hi. 

this is a rephrase of a question i posted earlier today. sorry, bit of a
newbie here. 

i have a scale bar in my application where each scale level is defined
in meters per pixel. i'd like to control what layers show up at each
scale level and therefore i need to calibrate my scalebar units with
those of the mapfile. 

so my question is what units do the minscale/maxscale values in the
mapfile represent? 

thanks for any helpful tips. 

matt.