A city radius map is the standard “everything within X distance of point Y” tool, but pre-configured for a specific city. Instead of typing an address into a generic mapping tool, you land on a page that's already centered on the city's most recognizable anchor (Times Square, the Loop, Charing Cross, Alexanderplatz, Shinjuku Station) with a sensible starting radius. From there you can move the center, change the radius, and export, the same controls as the main tool, just without the “find the address first” step.
The reason to maintain per-city pages instead of one generic interface is that what makes a radius useful is heavily local. A 10-mile radius from downtown Phoenix covers suburban sprawl that's functionally one continuous market; a 10-mile radius from downtown Manhattan reaches into four boroughs, crosses major rivers, and covers multiple transit-system catchment areas. The geometry is identical; the meaning isn't. City pages give you a starting frame that already reflects the local meaning, plus hand-authored content describing what does and doesn't fit inside the typical radii local planners and professionals use.
Each page is intentionally small in scope: one tool, one city, one set of coverage examples. You won't find auto-generated filler. If a city is listed here, someone looked at the geography, picked a landmark, ran through the common use cases, and wrote the page by hand.