The Charles Close Society for the study of Ordnance Survey Maps - some map covers
The best place to look for more information on Ordnance map covers is the superb book Map Cover Art by John Paddy Browne, published by The Ordnance Survey. It really is a lovely book and there is talk of it going out of print so obtain a copy as soon as you can.
This is a selection of map covers. The pictures indicate the markets they were aimed at with the earliest is aimed at cyclists and the later ones at Motor Cyclists and for the more affluent car drivers. Click on the small images to see larger versions and details.
A Bacon's large Scale Plan of Cambridge for cyclists and tourists
based on the New Ordnance Survey. Date approx 1900. This
is not an Ordnance Survey cover but it is included here to show
the type of cover that rivals to the OS were producing at the
time. 
An Ordnance Survey
White Cover with map. Compare this with colourfull Bacon map cover.
The content may have been superior but the cover does nothing
to entice the purchaser.
Motor Cycle at signpost by Ellis Martin 1919. Sheet 6A - 1/4 inch
to the mile map. 
Car passing signpost by Ellis Martin 1919. Sheet 15 1/2 inch to
the mile. 
Black car in profile by Arthur Palmer 1922. District Map of Cambridge
3rd Edition Large Sheet Series. 
Boulters
Lock by Ellis Martin on the Middle Thames. Boats are a
form of transport so it fits in here. This is the supreme cover
- click on the small map to see an enlargement of the cover and
an extract from the map itself showing Boulters Lock. These are
quite large images so they may take some time downloading but
the quality is wonderfull.
The
post 1940 covers were very austere by
comparison to the ones before.