[OpenLayers-Users] Questions: Projections, Google, Yahoo, etc

[Graham Davis]

Doing a little research, I can see that the metric system was designed 
specifically for mapping:

"All UTM grid systems divide the globe into narrow longitude zones. Both 
NATO or Warsaw Pact systems use zones six degrees wide. Along the 
central meridian of each zone, the grid coincides with the meridian. 
East and west of the central meridian the grid and meridians do not 
coincide because meridians converge.

The Metric System was defined so that the distance from equator to pole 
should be exactly 10 million meters or 10,000 kilometers. It isn't 
exactly, because the model for the shape of the earth in those days 
wasn't perfectly accurate, but it's quite close (actually about 10,002 
kilometers). So all UTM grid systems, NATO or Warsaw Pact, begin 
counting from zero at the equator.

The beauty of using longitude zones six degrees wide is that, at the 
equator, a zone is about 40,000/60 or 667 kilometers wide. Thus it is 
possible to create numbering systems so that distances on the grid in 
kilometers have at most three digits."

Taken from here:
http://www.uwgb.edu/DutchS/FieldMethods/UTMSystem.htm

-- 
Graham Davis
Refractions Research Inc.
gdavis at refractions.net


Graham Davis wrote:

>This *might* be useful in gaining more information on how various 
>projections work an why:
>http://erg.usgs.gov/isb/pubs/MapProjections/projections.html
>
>I've always known mercator as a "meters" projection, though I don't 
>really know why that is either.
>
>  
>