Which innovative retail product design change revolutionized the consumer map industry in the 1960s-70s, making road navigation significantly more user-friendly?

Maps have been essential tools for geography and exploration for centuries, but they've also evolved as retail products. From ancient hand-drawn maps to modern digital navigation systems, the business of cartography has transformed dramatically. This trivia question explores an interesting development in how maps were marketed and sold as consumer products in the 20th century - testing your knowledge of both geography products and retail innovation history.

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The accordion-fold map design that allowed drivers to view specific sections without unfolding the entire map
Waterproof map coating that prevented damage from rain and spills during travel
Color-coded highway systems that differentiated interstate routes from local roads
Phosphorescent ink that allowed maps to be read in low-light conditions without additional light sources