The difference between a "national park" and a "national monument" can come down to a simple matter of politics; the creation of a national park requires an act of Congress, according to the Sierra Club, while a president can declare a national monument without Congress under the Antiquities Act. Many of our most well-known national parks, such as Grand Canyon and Death Valley, started out as monuments.
Calculating the shortest path through every national park in the Lower 48 is no easy task. If you're a giant dork, you may recognize this as an instance of the Traveling Salesman Problem that looms large in computer science: Given X number of points, what's the shortest route you can take that passes through all of them?
Of course, the likelihood of anyone actually taking one of these mega-trips seems slim (if you do it, drop me a line). But the latest national parks trip seems quite a bit more practical than most, considering how many people plan epic road trips out west to visit multiple parks in a few weeks time.
If you're planning one of these trips for August, give Olson's map a gander before you hit the road.