City planning is a task that is often seen as a unique realm of governmental necessity.
The existence of externalities means that the market could create extremely sub optimal outcomes when creating a city.
For example, a house with a messy front yard hurts everyone, but the people in this house might have little incentive to clean up. A network of streets might not benefit its creator as much as the people who use it. While there are certainly some examples where the government intervening can be very helpful for most people, there are also many circumstances where government intervention is actually the key to a city’s demise.
The importance of city planning is so great that it truly cannot be the decision of any one individual.
Governmental city planning has many wins, but even more losses, not as a result of any specific government’s choices, but as a result of the institution’s inherent inability to capture information.