[OSM-newbies] Incorrect scale or longitude when exporting maps?

[luke.angel at clipsal.com.au]

Hi,

Maybe I am misunderstanding things, but something just doesn't seem to add 
up when choosing longitudes for exporting a map.
If I want to export two maps at significantly different longitudes, but 
the same scale and map size for each (1280 x 1024), shouldn't the 
longitudinal width (number of degrees) be different for each map?  I'm 
getting the same for each.

Here's the scenarios, both in Australia.

#1. Adelaide.
Select -34.6, 138.0, 139.61, -35.6536 at a scale of 1:500000
Exporting this gives a 1280 x 1024 image.

#2 Darwin.
Select -12.3, 130.0, 131.61, -13.555 also at a scale of 1:500000
Exporting this also gives a 1280 x 1024 image.

The latitude range varies with each (1.0536 vs 1.255 degrees), which is as 
per expected because of Earth's eliptical bulge near the Equator.
However, the longitude range is the same for each (1.61 degrees). Given 
this, I would expect the image width of each to be significantly different 
(Adelaide smaller as is further from the Equator where one degree 
longitude is less miles than nearer the Equator).

The scale of the images seem proportional so it seems to me that the 
longitude values for the images must be incorrect. How can the width of 
both exported images equal 1.61 degrees of longitude when one image is 
22.3 degrees further North than the other?

Kind Regards,

Luke Angel
Technical Communications Officer - Commercial Market
Clipsal Integrated Systems



Fifth Street
Bowden.  SA  5007
Telephone +61 8 8345 9509 
Facsimile  +61 8 8346 0573
luke.angel at clipsal.com.au



This email and any attached files with it ("this communication") are 
confidential and are intended solely for the use of the addressee. The 
unauthorised use, dissemination, forwarding, printing or copying of this 
communication is strictly prohibited. If you have received this 
communication in error, please notify us immediately by reply email and 
delete this communication. Any views expressed in this communication are 
those of the individual sender, except where the sender specifically 
states them to be the views of Clipsal Australia Pty Ltd. 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/newbies/attachments/20080630/84e9ab85/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 5974 bytes
Desc: not available
URL: <http://lists.openstreetmap.org/pipermail/newbies/attachments/20080630/84e9ab85/attachment.jpe>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 5962 bytes
Desc: not available
URL: <http://lists.openstreetmap.org/pipermail/newbies/attachments/20080630/84e9ab85/attachment-0001.jpe>