The predicted mine count in unzoned townships was over two times higher than that in zoned townships.
Christina Locke 2015, 'Frac Sand Mines Are Preferentially Sited in Unzoned Rural Areas.', PLoS ONEhttp://europepmc.org/articles/PMC4489872?pdf=render. Retrieved from PLOS CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)