Our goal is to make it so you can walk out of the house and within five minutes, you can find Pokémon. It may not be the most rare Pokémon in the world, but there’ll be a population of Pokémon living near all our players. Gyms will be a bit more rare. You want to find gyms so you can level up your Pokémon and battle there, so it will take a little more effort to get there.
Pokémon will live in different parts of the world depending on what type of Pokémon they are. Water Pokémon will live near the water. It may be that
certain Pokémon will only exist in certain parts of the world. Very rare Pokémon may exist in very few places. But you can trade. If you live in a place with lots of water Pokémon and you come to an event — we have these Ingress events that are getting bigger and bigger. We’ll have our biggest weekend ever on Saturday.
We’ll have events for Pokémon as well. Those are competitive, but they can also be places to trade stuff with other players. Pokémon trading is going to be huge. You can’t get all of them by yourself. If you want all of them you’ll have to trade with other players. Or you have to be someone who takes time off work and travels the world for a year. There may be people who do that.
Read more at
http://www.siliconera.com/2015/12/18/niantic-explains-how-pokmon-go-came-to-be-locations-and-item-distribution/#0D9kX2yfg7xBMP3u.99