It might be a reference to "seeing like a state", in which the author broadens the word "legible" to mean "readable by the state".
For example, a nice organised tree farm, where you chop down trees on 1/30 of the land each year, and loop around every 30 years has nice clear inputs and outputs, and is easier to assess than a old growth forest in which the local village has rights to some wood, but no one really measures what they cut or anything.
Under this meaning of the word, homeless people are invisible, or illegible to the state, as they don't have a fixed address.
For example, a nice organised tree farm, where you chop down trees on 1/30 of the land each year, and loop around every 30 years has nice clear inputs and outputs, and is easier to assess than a old growth forest in which the local village has rights to some wood, but no one really measures what they cut or anything.
Under this meaning of the word, homeless people are invisible, or illegible to the state, as they don't have a fixed address.