Story № 5 mapped gun homicide county by county and admitted the county map "understates its concentration by an order of magnitude." Here is the receipt: half of the gun homicide deaths in this data occur in neighborhood clusters housing about one in ten Americans — and inside Cook County, one in nine of its residents.
National statistics describe gun violence as an American problem; state data, as a regional one; county maps, as an urban one. Each zoom level is true, and each hides the next truth down. At the neighborhood level the pattern stops being a gradient and becomes something closer to a boundary: most census tracts in even the most violent counties record essentially no gun homicides, while a recognizable handful carry rates that would rank among the highest in the world.
Sort every neighborhood cluster in the country from most to least violent, then walk down the list adding up people and deaths. The curve bends hard: by the time you have covered one-tenth of the population you have covered half the deaths; by a quarter, three-quarters of them. Perfect equality would be the diagonal.
Within counties the same arithmetic holds, with one instructive wrinkle. Chicago's Cook County is the most concentrated of the big jurisdictions: half its deaths in places holding 11 percent of its people. Baltimore City looks least concentrated — not because its violence is evenly spread in any meaningful sense, but because its county boundary is the inner city: the safe suburbs that dilute Cook's denominator sit outside Baltimore City's line. Concentration depends on where you draw the box.
On the map, "concentration" regains its street names. The clusters carrying Cook County's burden trace the South and West Sides — Englewood, Garfield Park, Austin, North Lawndale — the same neighborhoods that anchored the life-expectancy story that opened this series. The North Side, miles away, has rates indistinguishable from the suburbs.
Split Cook County's neighborhood clusters into ten groups by their homicide rate and read across this series' other measures. The most violent decile is also the most deprived (mean ADI percentile 73) and the shortest-lived (71.1 years — a full decade below the safest decile). Gun violence is not a separate map from disadvantage; it is the sharpest engraving of the same one.
If half the problem lives with a tenth of the population, then national averages are the wrong unit of action. This is the empirical core of community-violence-intervention strategies — focused deterrence, street outreach, place-based investment — which consistently target blocks, not cities. It is also the human core of this book's argument: a child's exposure to violence is not an American statistic or even a Chicago statistic. It is an address.