Ex Raid Gym Criteria

Can someone share in depth details of how to trigger a Gym to Qualify for Ex Raid Candidate? Also, I have a few Gyms which as per Gmap are on green area, but POGO map does not reflect it (green patch- which I guess is one of the criteria for Ex Raid).
Thanks in advance.
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On here, no.
Officially you're not meant to manipulate things like trying to create an ex raid gym etc.
Also this topic has nothing to do with Wayfarer, which is the system for submitting POIs in all Niantic Games.
Unofficially, go to reddit or just Google "how to create an ex raid gym" and you'll get all the information you need
First of all, Pokémon GO uses data from Open Street Map. What "Gmap" has on an area is irrelevant. Secondly, the area need not necessarily be "dark green" in order for a particular gym to be EX. Certain areas of farmland can result in a gym being an EX gym, e.g. an orchard, if memory serves. Beyond that, I suggest looking on somewhere like The Silph Road as your question is only marginally related to Wayfarer, but I do appreciate there are no official Pokémon GO forum.
Agree with Ascarlet. Its generally if a gym opens in a spot where its a dark patch of green in the game. They tend to be in park areas
A good rough and ready rule of thumb is if a nesting species spawns at the waypoint it has the potential to be an exgym.