None of this is illegal, and collectively we seem resigned to it. These are subtle gestures, but they’re becoming ubiquitous. (There are many far less subtle examples, such as the “pee paint” deployed in cities like Hamburg and San Francisco, which makes urine bounce back at the offending urinator.)

Ms. Theodore recounted that Heinrich Zille, the early-20th-century illustrator and chronicler of life in the Berlin tenements, once said something like “You can kill a man with an apartment as with an ax.” The same could probably be said about a map: 1930s residential security maps (through redlining) cut off entire neighborhoods from investment, rigging the game against those neighborhoods’ mainly nonwhite residents.

The fact that life expectancy in Baltimore’s poorest ZIP codes is about 20 years shorter than in the richest ones, Ms. Theodore says, “is certainly not the result of ‘bad choices’ on the part of poorer residents, but is the direct result of earlier planning decisions. So, yes, space matters, and sometimes it is being used as a weapon.”

Tools of exclusion aren’t new, but we are gaining a much more comprehensive understanding of the innumerable ways they are being deployed. Richard Rothstein’s recent book “The Color of Law: A Forgotten History of How Our Government Segregated America,” for example, shows how policy pursued by the federal government after World War II was designed to subsidize the development of suburbs on a condition that the homes be sold only to white families and that deeds prohibited resale to African-Americans.

Mr. Rothstein’s writing is measured, but everything he relates is chilling in its deliberateness and intent. Page after page reveals the extent to which segregation was implemented, resulting in the divisiveness that so characterizes us today.

“The Arsenal” goes less deep but broader, addressing private, public and shared spaces. A series of essays by Interboro and in-the-trenches contributors show that the ways we plan and design our built environment, and allow (or forbid) access to it, have a serious impact on everything from economic mobility to public health.