When in doubt, put it to the t-test.
I liked the torus
The passport map may have several patterns showing on it.At a rough guess, there may be two patterns. One is border-States have higher rates of passport-holders than non-border States.The other is that certain States have large cities with good airport access to overseas destinations.Some States sit in both categories.And then there's a little room to argue about definitions. Do water-borders count? What about rivers vs. lakes as a water-border? Kind of fun to think about.
I also think there's also some correlation with median income...all the states with 30% or less seem to be those that normally appear in the bottom quartile on household income lists.
And that explanation may be better than the ones I offered in category 2.Though the explanations I offered are strongly related to median income...There may still be outliers in the bottom quartile, though those appear to be land-border States.