Apparently it’s something that’s starting to exist:
Day hiking within city limits isn’t a new concept, of course. There are guidebooks detailing trails in cities from San Francisco to Atlanta. But Thomas has pushed the pursuit further, mapping out routes as long as 200 miles from one corner of a city to another and using infrastructure like stairways and public art to rack up elevation gain and provide something approximating a vista. She started in 2013 with a 220-mile through-hike in Los Angeles called the Inman 300, named for one of its creators, Bob Inman, and the initial number of stairways it included. Among other efforts, she has since hiked 60 miles through Chicago, 200 miles in Seattle, and 210 miles in Portland, Oregon. In 2015, she trekked the 54 miles from Selma to Montgomery, Alabama, on the 50th anniversary of that historic civil rights march.
The way I see it, urban thru hiking lets you walk more comfortably with less gear since you never need to make camp. Routes that amount to a serious sustained hike can be added up from segments which avoid car traffic as much as possible, and which link up with public transit to let you get home at the end of the day and back at the trailhead easily the next one.