I think this article touches on some of the issues you raise, although 
not confined to the circumstance of traffic maps: 
https://blogs.esri.com/esri/arcgis/2012/02/14/map-orientation-when-true-north-is-not-at-the-top/ 
.

                  Joel Kovarsky


On 9/16/16 8:53 PM, Michael Holt wrote:
> I have "Supplemental Map - Routes through Richmond, Virginia."  It was 
> drawn in 1950 and my copy was last updated in 1955.  It depicts the 
> major roads that go all the way through the city proper.   The map is 
> 26 inches wide and 21 inches high; the orientation is taken from the 
> orientation legend and the street names.  I cannot believe the 
> difference between height and width is due to any difference in the 
> city's layout: it's just not much different in real life.  Is having 
> north to the left a convention on older city traffic maps?
>
> Michael Holt
>
>
>
>
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