When the zombies come, it will be helpful to know just how long you have to grab guns, hop in your bite-proof S.U.V., and get the hell out of wherever you live. Thankfully, there’s a map for that now. Zombies USA is an online simulation that lets users place zombies, change how fast they can move, and manipulate their bite to kill ratio. If zombies first occur in Detroit, for instance—and why wouldn’t they?—this map lets users figure out how long it would take for the slow-moving munchers to hit Chicago, New York, Miami, and so on. The map also helps users answer questions like, “if zombies broke out in Maine, would I be safer in Seattle or San Diego?” Ultimately, Zombies USA is a bit of a lark, a speculative tool for worst-case scenarios, but it’s still fun to mess around with. And, hey, who knows? It could come in handy.