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Maps unlock the world in front of us...even if we're not standing right in front of the landscape contained on the map we're gazing at. They allow us to wander through the landscape, cross mountains, ford rivers and streams, and envision campsites in the backcountry. And, in the case of a new eBook, they allow us to look into the past of some national park settings.

In an atlas holding a dozen or so yellowed maps, Dave Broer allows us to take a decades-old look at parks such as Crater Lake, Great Smoky Mountains, Grand Canyon, Glacier, and Mammoth Cave...before it was a national park...in a compilation he's created for national park junkies.

Historic Maps of the National Parks of the United States ($4.99), features maps from the early 1900s up to mid-century. Drawn in many cases by U.S. Geological Survey cartographers with some roads and trails added by the National Park Service, the maps, when compared to today's maps, quickly show changes time has brought to the parks.

Take the map of Mount Rainier, for example. The Russell Glacier, which these days falls short of reaching Echo Rock, wrapped around that feature and stretched towards Seattle Park when the map was drawn in 1938. There is no Skyline Drive on the 1934 edition of the "proposed" Shenandoah National Park. Many Glacier was still a "chalet," and not yet a "hotel" in Glacier National Park.

For long winter nights, rainy afternoons, or in the lodge after a day in the park, these maps bring an added, interesting, perspective to the parks.