The council, spearheaded by Jeremy Nutting, is looking to remove the city at large from the game. Even though this technically can't be done, since the game is based on map data (and it doesn't make much sense), the best that could be done is possibly remove Poké Stops or something to that effect.
The idea sprang up after the City Council had a meeting about the droves of teenagers and other players walking around idly, looking down at their phones while crowding the marina and other areas, making noise, littering and partaking in certain legal and illegal vices.
After discussing Pokémon Go and the burden it seems to be placing on the city, the council members voted unanimously to request that the entire area "opt out" from the game, as far as public places and parks in Des Moines. Local business, as Nutting commented, were being affected by these roaming crowds. A valid worry, especially if the crowds of players are as obtrusive as described, but something a ban on one mobile game isn't going to solve immediately.
It's highly likely this request simply won't be fulfilled due to the large expanse of area and the fact that these are public areas being policed, essentially. A similar situation occurred in France recently when the mayor of a French town decided he was interesting in "banning" Pokémon Go from the city.
It seems both mayor Fabrice Beauvois and council member Jeremy Nutting subscribe to the same school of thought when it comes to the mobile game: Augmented reality games are "spreading" and the perceived problems aren't just going to go away.