I've had the same thoughts. Roads are basically moving around cars, which move people and resources. This is the same function as red blood cells. This analogy

I've had the same thoughts. Roads are basically moving around cars, which move people and resources. This is the same function as red blood cells. This analogy includes white blood cells-- highway patrol police. People are perhaps the oxygen which is the catalyst for everything to work, and the resources like food, materials, etc., are like the nutrients the human body needs. Buildings are also individual cells of different kinds, and you can see different buildings have different functions as well, just like cells. I think cities are clusters of cells, and just like clusters of cells in the body, they perform functions that could, in turn, categorize them as "organs", because there is a dominant industry in that city, and the buildings in that city serve specific functions that get exported out to the rest of the cities in the country or the world. I think the paper's analysis is interesting, but I also think the starting point for the analysis should be function and not hierarchical structure, which is mostly static.