Before creating Pokemon Go Niantic made two other games Field Trip and Ingress Ingress: The game that reveals Google’s secret war to control London (We loved reading about Operation Sitrep: A Series of Tubes).
One article in this collection, Pokemon GO, A Popular Game with Some Troubling Consequences, is critical of the location of Pokestops. This article assumes the location of the Pokestops is software driven, but in actual fact were crowdsourced by people who played Ingress.
The Candidate Portal criteria for these portals can be found in this collection:
As of September 2, 2015, we will be temporarily suspending new Portal submissions for a period of time while we work on processing the backlog and on designing new and more efficient ways to evaluate Portal submissions and edits. You will no longer see the NEW PORTAL option when long pressing on the Scanner.
In order to help us address our growing queue of new Portal submissions, starting Dec 31, 2014 we will temporarily suspend the Seer Medal. You will maintain your current Seer Medal status Ingress Portal Map