How is data serialized when the level is saved in the editor?

Hello all,
We’re developing a tile-based game and I want to generate the tiles in editor and store them in the level. I somewhat did this by using a TArray uproperty but I actually want to use a TMap which is not supported by blueprints. So I want to know how the data on instances of actors in the editor is saved into the level and loaded back when the editor is started.

Currently, if I store the tiles in a TMap, they don’t survive when I restart the editor.

Thanks in advance.