Society’s transition toward more sustainable energy sources is well underway. But substantially reducing the use of fossil fuels to generate electricity, to power vehicles, and to manufacture the stuff of everyday life will profoundly disrupt the communities that currently dedicate themselves...

In recent empirical literature on spatial agglomeration, many papers find evidence consistent with location-specific externalities of some sort. Our willingness to accept evidence of agglomeration economies depends on how well key estimation problems have been addressed. Three issues are...