There isn't any real discussion of what this picture is telling us. I'll treat it like a Rorschach test:
- I immediately see a "blue state/red state" divide. Those liberal bastions on each coast hold the passports while the conservatives hunker down and refuse to admit that this is a world out there beyond America's borders. The passport is a symbol of your "cosmopolitanism".
- I see a rich/poor divide. Those states with high median incomes have higher proportions of passports than those will low incomes. The passport is a litmus test of wealth vs. poverty.
- I see a rural/urban divide. Those states of the Deep South and the Appalachian backwoords have significantly less passports. These are the areas of poor schools and rednecks versus the coasts which provide more urbane education with an outward looking perspective that makes people more eager to travel and enjoy world culture.
- I see a high tech/low tech divide. Those states with high tech industries and sophisticated manufacturing have better educated, more prosperous workers more willing to travel the world and explore possibilities.
- I see a historical North/South divide. Those states of the Old Confederacy are more inward looking, one happier with their "peculiar institutions" and their distinctive "culture". Those of the old North and the the modern expression of that culture on the West coast have passports because they are more of a mercantile, worldly-engaged people looking to trade around the world and learn from many cultures.
And I can come up with some wilder interpretations: Arizona (and the broader Southwest) has a high passport rate because its latino population has more links to relatives across the border in Mexico so they have a greater need for passports to travel the border. Similarly the states bordering Canada have a slightly higher passport rate because these people more frequently cross in to Canada than the rest of the American population.
Who knows the truth. But it is fun to speculate.