This post card, post marked 1925, shows the boat main house that no longer exists. Boating was one of the principal reasons to come to Miami. Before the house was finished, Mr. Deering commissioned 2 boats for his use. There were several other boats as well as 10 employees just to work on boats. The senior captain Joseph Santini had living quarters upstairs in the boat house for he and his wife.This survey, from when the estate was intact, shows the boat house on the circle.
I'm not sure but I would guess the circle in this modern day Google satellite image is the same circle built with the boat house. You can also see the channel Mr. Deering had dredged for boats to approach centered on the house.
Today the Ermita De La Caridad sits at the circle's center with Mercy Hospital around it.
This painting by John Singer Sargent Basin with Sailor, Villa Vizcaya
Miami, Florida may have the boat house as it's back drop.