Various reports claim that Pokemon are more likely to be found in their appropriate environments, such as water types near water. Is this true, or is it just observation bias with pseudo-random placement?
If true, what are the preferred places to find each type?
(Bug, Dark, Dragon, Electric, Fairy, Fighting, Fire, Flying, Ghost, Grass, Ground, Ice, Normal, Poison, Psychic, Rock, Steel, Water)
Pokemon spawns are very much affected by location.
The real world is split up into a number of biomes. Spawn chances, rates, and available Pokemon are very much biome dependent. This data is likely pulled from Google Maps and Ingress, with some minor alterations.
For example, it is far more likely for a Muk to spawn in an Urban environment than it is for it to spawn in a Meadow.
It's true to an extent. Walk by river, you'll see lots more magikarp and psyducks, forests seem to contain grass type/normal type/and pikachu's, towns are generally bug type/normal type/flying type. Rock types are pretty random, haven't really found a good spot to farm them yet, same for electric and fire. They are seen pretty randomly. I don't know about ghosts being near graveyards, but I know you'll find them at night randomly as well.
Go to this link, there is an article that explains where you can find the different types of Pokemon: https://www.vg247.com/2016/08/25/pokemon-go-where-to-find-pokemon-types/
Just in case you can't access it, for some reason, here's the list:
Normal - More or less everywhere - that's why they're called Normal
Fire - Residential areas and neighbourhoods, warmer areas like beaches
Water - Rivers, streams, lakes, harbours, beaches - anywhere where there's water
Grass - Farms, forests, and parks are good options, as are gardens and golf courses
Bug - Farmland, woods and forests, gardens and generally grassy areas like parks, nature reserves, smaller pathways, golf courses and playgrounds.
Rock - Quarries, towns, parking buildings, train stations, highways, or large buildings such as shopping malls
Ground - Ditches, streams, parking garages, playgrounds, railway stations, roads and generally urban areas.
Electric - Industrial parks, schools and college campuses, and other dry places that are largely concreted over
Fighting - Sports centres and stadiums, and they’ll also congregate around larger gyms.
Poison - Ponds, marshes, lakes, more industrial areas of cities and in large buildings
Fairy - Places of interest (local landmarks), churches or the cemetery.
Flying - Farmland, forests, woods and grassy areas such as nature reserves, playgrounds, parks and gardens.
Dragon - Famous places or landmarks
Ghost - Occasionally around churches, but they’ve also been reported to show up in built-up residential areas such as parking lots at night.
Ice - Grassy areas occasionally and near bodies of water more often than that. You’ll of course also find them anywhere there’s actual snow and ice.
Psychic - Grassy areas, but that’s pretty uncommon in general. Some also show up in residential areas but seemingly only at night. A better place to more reliably find them is in and around hospitals.
Steel - Inside or around larger building structures. They can also be found near railway stations and tracks.
Dark - In cinemas and theatres.
