The economic efficiency is demonstrated by the greater job growth in urban areas. I'll easily find stats on this when I get off mobile. And this is the first time I've heard someone claim that sprawl and dispersed populations are environmentally better than urban areas. Not only do dispersed populations need greater land development, they need significantly more energy used in transportation to deliver the same quality of life. I saw a stat that compared the per capita carbon footprint of wealthy countries and it was essentially inversely proportional to levels of urbanization. And like the economy one, sit tight for an hour or do for me to get home and share this data.
Sources for greater economic growth in urban areas:
https://www.ers.usda.gov/topics/rural-economy-population/emp...
Countries by CO2 emissions per-capita: https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...
Countries by urbanization: https://en.wikipedia.org/wiki/Urbanization_by_country
And that's not even getting into things like the amount of land that gets developed for low density homes and services, roads, water reservoirs, electric lines, etc.
Wealthy rural countries (USA, Australia, Russia), produce more carbon than dense wealthy countries. Granted, I wouldn't be surprised if carbon emissions and environmental impact of the average city resident was higher than the average rural resident - but that's largely a result of the fact that rural residents are generally less wealthy. This is definitely true on a global scale (the countries with the lowest carbon footprints are poor, rural ones), and I wouldn't be surprised if it were true on a nation wide scale. I didn't explicitly state it in in the first post, but I did clarify in the second that this was for the same standard of living.
On a side note, an interesting thing to look into is how Singapore manages to provide so much services with such a small budget - 14.2% of GDP per capita as opposed to 26% in the US. A huge part of this is because it's so much more efficient to provide services when you're dealing with population concentrated in such a small area. Imagine how much more money (and energy) it takes to deliver electricity, running water, sewage, emergency services, education, etc. to households in Oregon where 4 million people are distributed across 98,466 square miles as opposed to concentrating them all in 278 square miles. Even if things like land and labor cost more, so much overhead and operational costs are saved by not having to service such a massive area.