Ratata, Pidgie and Zubats are everywhere but where do you find the Pokémon you really want? The especially rare and powerful ones such as Dragonite and Gyarados are not easily found, but can be evolved if you find enough of their original forms.
While lures can often attract hard-to-find Pokémon, there are some Pokémon you are almost guaranteed to get in some areas and we personally checked them out. Apparently Pokémon nests, or places where some species will spawn more often do exist.
Here's a list of important Pokémon and near-guaranteed locations where you'll find them.