Why are cops called Flat Foots?

Question

I was watching All in the Family on youtube and Edith Bunker called the cop a flat foot?

What did she mean by calling him a Flat Foot?

Answer 1

 In the early part of the 20th century, New York policeman as well as other larger metropolitan areas employed patrols on foot..............they walked so much some acquired fallen arches, thus "flat feet". Since that time, foot patrols have been slangily referred to as 'flat foots".