FIRMAMENT : EXPANSE OR SKY.
Genesis 1:7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
Revelation 22:1–5 And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations. And there shall be no more curse: but the throne of God and of the Lamb shall be in it; and his servants shall serve him: And they shall see his face; and his name shall be in their foreheads. And there shall be no night there; and they need no candle, neither light of the sun; for the Lord God giveth them light: and they shall reign for ever and ever.
What is located under the firmament/sky? Earth.
What is located above the firmament/sky? Heaven.