it's a picture of The Church and New Jerusalem.
the same city john saw.
Ezekiel 40:1-2
“In the twenty-fifth year of our exile, at the beginning of the year, on the tenth of the month, in the fourteenth year after the city was taken, on that same day the hand of the LORD was upon me and He brought me there. In the visions of God He brought me into the land of Israel and set me on a very high mountain, and on it to the south there was a structure like a city.”
Revelation 21:10
“And he carried me away in the Spirit to a great and high mountain, and showed me the holy city, Jerusalem, coming down out of heaven from God,”