Hitting the road is in our genes - even the first Americans had to cross the Bering Straits. The invention of the automobile only aided and abetted our wanderlust (next stop Mars?). But, of course, we need directions on how to get to wherever it is we want to go, so the road map was born.
Now a popular collectible, most road maps until the 1970's used to be given away for free by gasoline companies, automobile clubs, and state and local government agencies, as advertising to promote their products, services, and tourist destinations.
Throughout the 20th century, tens of thousands of different maps were printed. Some were merely decorated with a company's logo, while others also offered colorful photos or graphics. The sheer variety allows collectors to concentrate on particular categories without fear of ever running out of new "finds."
Some collectors devote their resources to a particular state or vacation spot. Some seek out a particular company's logo, like the Standard chevron or Esso oval. And others focus on a year of personal interest (birth dates are popular).
As ephemera, road maps in fine+ condition can be difficult to find as they were frequently folded and re-folded to the point that the paper would tear and separate along the fold lines, or they were soiled by grimy fingers or spilled coffee.
Of course, the best way to store a road map is open and flat (as at the Library of Congress), but few collectors have the space, so it is permissible to keep them in archival storage bags (PVC-free) or boxes (acid-free). Dirt and grime can often be removed with the aid of an art eraser or white bread (http://auctionbytes.com/cab/abu/y200/m04/abu0011/s04#s02). And never display a map in direct sunlight, as it will fade and change color.
An affordable collectible - most maps can be had for less than $20 - road maps can be found at yard and estate sales and online at many commercial and auction sites. Of course, it always helps to know what you're buying (or selling), so if you're interested in this collectible, check out the following web resources:
Website Resources
PetrolMaps
http://www.ianbyrne.free-online.co.uk
For the collector of British/European road maps.
Road Map Collectors Association
http://www.roadmaps.org
http://www.roadmaps.org/links/index.html
Excellent site offers history, newsletter, events, more. Check out their great links page!
Twentieth Century Maps
http://www.20thcenturymaps.com
This commercial site is excellent for searching their catalog of 10,000+ maps. Also has sections on storing maps and deciphering date codes.
Western Association of Map Libraries
http://www.waml.org/datecode.html
Extensive list of date codes.
