This is one sandwich with seven names, and the names are the whole subject. Submarine, sub, grinder, hero, hoagie, wedge, and po' boy describe the same object, a long split roll built the length of itself, but the word a person reaches for is a map coordinate. Say "hoagie" and you are placed in Philadelphia. Say "grinder" and you are in New England. "Hero" puts you in New York, "wedge" in the lower Hudson Valley, "po' boy" in New Orleans, and "submarine" or "sub" almost anywhere the chains reached. The thing being named never changes; the naming is the regional argument, conducted one word at a time, and every region is convinced its word is the real one.
The interesting fact about the atlas is how little the names track real differences. A few are genuine: the po' boy rides a distinct New Orleans loaf and the grinder leans toward a hot, toasted reading in much of New England. But most of the boundaries are linguistic, not culinary. A Philadelphia hoagie and a New York hero, built cold and Italian, are the same sandwich under two words, and the dressing differences locals defend hardest are often smaller than the differences between two shops in the same city. The map is a dialect map. It records waves of Italian, and in New Orleans French-Creole, immigration settling into different cities and naming the same long roll in different mouths, then defending the local name with a fervor the sandwich itself does not require.
Each name also opens onto its own codified builds, the cold Italian, the hot parm and meatball, the dressed fried-seafood po' boy, the chain assemblies shipped nationally, and each of those is a real sandwich with its own rules worth treating on its own terms. They deserve their own articles rather than being crowded in here, because the point of looking at the family as a whole is not the fillings. It is that a country can take one simple idea, a long roll packed end to end, and turn it into seven words that each function as a way of saying where you are from.