The world map shows PokeStops, Gyms, and wild Pokemon near the player. Rustling leaves in an area indicate where Pokemon are roaming. If players enter this area, wild Pokemon should start turning up after a few minutes. Note that Pokemon can still show up outside of these areas.
If a PokeStop is raining pink petals, it means someone has used a Lure Module, which increases the frequency of wild Pokemon appearing near that particular stop. Stay close to a PokeStop if you want to get the most out of its Lure; even better, get between two overlapping PokeStops with Lures on them for a greatly increased rate of wild Pokemon showing up.
Originally Posted by: gamespot.com