Nuclear electromagnetic pulse is not one circle on a map. Yield, burst height, and latitude change the footprint and the intensity. A detonation in space can illuminate a continent-scale area with a field that varies sharply from the center to the edge — the often-cited “smile” pattern in northern latitudes, stronger south of ground zero than directly underneath.

That pattern is why a single red circle over the middle of a country is a cartoon. Intensity is not a flat disk. It can be stronger in a band offset from the point under the burst, which is the smile people cite, and weaker where a flat circle would have you expect the worst. Latitude changes the picture again. You do not need to pick a height to stop treating the map as one ruined downtown in the middle.

That geometry is why slogans about “one bomb over Kansas” are sketches, not forecasts. The sketches are still useful. They show that the attacker, if there is one, is aiming at infrastructure, not at a skyline.

A sketch can be crude and still teach the category: a wide insult to things that conduct, not a crater you can drive around. A forecast would need a yield, a height, and a location this briefing does not have and will not invent. The sketch’s job is to keep the conversation on transformers, communications, and the restart, rather than on a single city block.

Civil defense that only imagines a crater downtown is preparing for a different war than the one this physics describes.

Downtown-crater plans stock for blast and fire in a dense core. Those are real subjects for other hazards. They are the wrong sole picture for a burst whose serious public effect is a field over a region, with the damage concentrated in long lines and electronics rather than in one neighborhood’s buildings. Preparing only for the crater leaves the wide case unnamed.

The civilian response to the wide case looks dull next to the physics: spares, relays, black start, water, a radio, a utility that will explain a deliberate trip. The altitude discussion matters because it tells you which list to be on. It is not an invitation to speculate about a weapon and call that a plan.