Nests are areas that a specific specie appears regularly and frequently. A player can easily find and capture a particular wild Pokemon. Tap the link below to see the details of Pokemon nest.
Pokemon nests in Pokemon Go | PokemonGo
Here are the list of Gastly nests. Some of them are confirmed by players but others are rumor. Go Radar map screenshots are put to see how often Gastly can be found in each location.
To see the details of Gastly, tap the name of the Pokemon above.
Gastly | PokemonGo
For the nests of each Pokemon, tap tap the name of Pokemon in the chart below.
Dratini nests and spawn locations
Lickitung nests and spawn locations
Eevee nests and spawn locations