[ka-Map-users] scalebar question 1cm = 1km?

[Donal Regan]

Thanks.

I think 

2) Don't tell anybody what the scale ratio of your map  is, and rely on the scale bar for relating display distances to map  distances.

is the way forward.



Tim Schaub <tim at commenspace.org> wrote:     Hey Donal-
  
 MapServer assumes a monitor resolution of 72 dpi by  default (so this is what the scale bar assumes by default).  This is seldom  correct.  The upshot is that the scale ratio (1:1000000) is seldom  correct.  However, this doesn't really matter unless you advertise the  scale ratio and a client with a non 72 dpi monitor takes out a  ruler.
  
 There are two things that you can do if this bothers  you.
 1) Guess at your client's resolution and modify the  scale bar's resolution property (myScaleBar.resolution =  96).
 2) Don't tell anybody what the scale ratio of your map  is, and rely on the scale bar for relating display distances to map  distances.
  
 Since people always toss around numbers like 1:250000  for map scales, it might be disappointing to hear that these numbers aren't  generally accurate for monitor displays (since there is not a reliable way  for the server to know the client's screen resolution ahead of time).  This  is why I think it's better to rely on a scale bar than a numeric  scale.
  
 Tim
  

       
---------------------------------
   From: ka-map-users-bounces at lists.maptools.org    [mailto:ka-map-users-bounces at lists.maptools.org] On Behalf Of Donal    Regan
Sent: Wednesday, June 21, 2006 1:48 AM
To:    ka-Map-users at lists.maptools.org
Subject: [ka-Map-users] scalebar    question 1cm = 1km?


   
Hello all.

I am displaying a map that has amongst it's    scales 1:100000. I would expect my scalebar to show 1cm = 1km, i.e if  I    physically measure the scalebar with a ruler, 1cm on the ruler would    correspond to 1km on the scalebar. However, I'm finding that 0.9cm = 1km ,    1.85cm = 2km  up to 5.7cm = 6km.


 Is this just the way it    is or am I misunderstanding the way the scalebar should be    working?

Cheers,

Donal.

      

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