Rashi: It is an expression of Mechugah (compass), i.e. Ogel (a circle). Radak - the earth is in the middle, and Shamayim is like a circle drawn around it. Later, the verse mentions Shamayim; the matter is repeated in different words.

Radak: This is an anthropomorphism. Hashem has no place. It is as if He sits on a very high place, and looks at the lower world.

Targum Yonasan: He makes dwell in a high place the Shechinah of His honor. Radak - he explains ha'Yoshev like ha'Moshiv (makes dwell).

Malbim: Some people depict Hashem sitting in Shamayim, and the earth is His footstool. Some depict Him like a king sitting and camping among them, and Shamayim is like a tent spread above. If you think that He sits in Chug ha'Aretz (Shamayim, which is a sphere surrounding the land), the land's residents are like grasshoppers, due to their distance.

Rashi: In front of Him, they are like grasshoppers. Radak, Malbim - since He sits on a very high place, what is below looks small - "va'Nehi v'Eineinu ka'Chagavim v'Chen Hayinu b'Eineihem" (Bamidbar 13:33).

Rashi: [He spreads] like a curtain. Radak - this is like "va'Yimtachem ka'Ohel" later in the verse. He spreads it for dwelling below. Man does not dwell in a house without a roof!

Malbim: If you think that He spread Shamayim like a thin tent above, and He dwells below it, like a king dwelling amidst his nation... (refer to 40:23:1:3, 40:23:2:2).