The Rigveda mentions in several places that Vishnu measured out the Earth:
1 "I will declare the mighty deeds of Viṣṇu, of him who measured out the earthly regions, Who propped the highest place of congregation, thrice setting down his footstep, widely striding."
2 "For this his mighty deed is Viṣṇu lauded, like some wild beast, dread, prowling, mountain-roaming; He within whose three wide-extended paces all living creatures have their habitation."
3 "Let the hymn lift itself as strength to Viṣṇu, the Bull far-striding, dwelling on the mountains, Him who alone with triple step hath measured this common dwelling-place, long, far extended."
In fact, the measuring out of the Earth by Vishnu with three steps is a motif that occurs in many, many places in the Yajurveda, and the Samaveda, and also in many other places in the Rigveda itself.
Well, these Rigvedic verses indicate that it was Varuna, not Vishnu, who measured out the Earth:
"I will declare this mighty deed of magic, of glorious Varuṇa the Lord Immortal, Who standing in the firmament hath meted the earth out with the Sun as with a measure."
"Lord of all wealth, the Asura propped the heavens, and measured out the broad earth's wide expanses. He, King supreme, approached all living creatures. All these are Varuṇa's holy operations."
So who measured out the Earth? Was it Vishnu with his three steps, or was it Varuna? (I was reading one of Keshav Srinivasan's questions: "Who is addressed as "the step of Vishnu" in the Yajur Veda?" He said that the three steps of Vishnu refer to an avatar of Vishnu--Vamana the dwarf--who "made the Earth safe for humanity" by defeating the demon Mahabali by taking three steps. Does this have something to do with the answer to my question?) Or did Vishnu assign the task of measuring out the Earth to Varuna? This seems unlikely, since the Vedas say that Vishnu himself took three steps to measure out the Earth. Or was Varuna the one who measured out the Earth, and all references to Vishnu references to Vamana?
Also, as a side question: why does Rigveda 8.42.1 refer to Varuna as an asura?