What you need to know about biomes in Pokémon Go
Pokémon Go has biomes now, but not too much is known about them. We list out all the known biomes and explain how they work.
This article references relevant content from the polygon.com website. Original article link: [https://www.polygon.com/pokemon-go-guide/24140393/biomes-map-city-mountains-forest-beach-spawns]

Pokémon Go has added a biome system to the game, making it so some Pokémon, like Wiglett, only spawn in certain areas.
Those hunting for specific Pokémon will want to head over to these biomes, but they seem a little bit finicky at the moment, with not much known about them. In fact, it’s enough of an issue that players are inventing fake beaches to create their own Wiglett spawns.
Thankfully, you don’t have to go that far if you know where to look. We explain how many different biomes there are and how spawns work within biomes, based on our own experiences.
How many biomes are in Pokémon Go?
There are four confirmed biomes in Pokémon Go. These are the ones that Niantic have posted about:
There are a few other biomes that are unconfirmed in official name and type:

There may be more than this, but these are ones we’ve encountered.
Do some Pokémon only spawn in specific biomes?
As previously mentioned, Wiglett only spawns in beach biomes. The biomes confirmed by Niantic also had some specific spawns during the “Rediscover Kanto” event, according to their Rediscover Pokémon Go page. From what we can tell, the following biome spawns aren’t still boosted (except Wiglett, which remains findable in beach biomes), but you can see what the spawns were below, for reference:
Pokémon Go biome map tools
In-game, it’s hard to tell where biomes are at a glance, so at present the community is filling in the gaps with their own resources, especially in light of Wiglett being beach biome exclusive.
It appears that Pokémon Go’s map pulls data from OpenStreetMap, which tracks biomes using surveys, aerial images, and other sources. Since this is an open platform, the community has made several tools to browse beach biomes:

It’s likely more community-run biome maps will emerge over time — especially as more biome-exclusive Pokémon are introduced to the game.