With around 10 million people within its nearly 300 square miles, according to the C.I.A. World Factbook, Tehran is comparable in density to New York City. About one in 10 Iranians lives in Tehran proper, and millions more live in its greater metropolitan area. Photos and videos taken in the capital in recent days show long lines of cars at gas stations and congested traffic on the roads as people try to flee. The sense of fear escalated on Monday evening after the Israeli military issued an evacuation order for a zone in District 3, a densely populated upscale residential center of several hundred thousand people. Hours later, President Donald J. Trump also warned in a Truth Social post that the entire population of Tehran should “immediately evacuate.” And on Tuesday, the fifth day of back-and-forth attacks, the Israeli military issued another evacuation warning for an area that covered part of District 18. That district is just south of the Mehrabad International Airport, and is one of the poorest neighborhoods in Tehran. The Israeli military said that it had targeted military and critical energy infrastructure, particularly the facilities and resources Iran needs to build nuclear weapons. The New York Times verified strikes in both dense residential areas, including the cities of Tabriz and Mashhad, and less populated areas, like Natanz, which is home to Iran’s largest uranium enrichment center.