It's a little more complicated -- if living in a city means that you switch from a car to public transit, that's a major environmental win. If living in a city

It's a little more complicated -- if living in a city means that you switch from a car to public transit, that's a major environmental win. If living in a city means you switch from a free-standing house to an apartment building, that's a smaller but substantial environmental win. Sewers are generally better than septic tanks, trash collection is more efficient when people live closer together, and so on. Cities concentrate pollution and completely overwhelm the local environment's capacity to absorb human impacts. However, they generally reduce overall pollution when compared to suburban or rural living at the same income level.