Who hath laid the measures thereof - That is, as an architect applies his measures when he rears a house.
If thou knowest - Or rather, "for thou knowest." The expression is wholly ironical, and is designed to rebuke Job's pretensions of being able to explain the divine administration.
Or who hath stretched the line upon it - As a carpenter uses a line to mark out his work; see the notes at Isaiah 28:17. The earth is represented as a building, the plan of which was laid out beforehand, and which was then made according to the sketch of the architect. It is not, therefore, the work of chance or fate. It is laid out and constructed according to a wise plan, and in a method evincing infinite skill.

Who hath laid the measures thereof - Who hath adjusted its polar and equatorial distances from the center?
Who hath stretched the line - Who hath formed its zones and its great circles, and adjusted the whole of its magnitude and gravity to the orbit in which it was to move, as well as its distance from that great center about which it was to revolve? These questions show the difficulty of the subject; and that there was an unfathomable depth of counsel and design in the formation of the earth.

Who hath laid the measures thereof, if thou knowest?.... Did God or a creature? The Lord, no doubt. He laid them out in his divine mind, and laid them forth by his divine power; who does all things by weight and measure. He fixed the dimensions of the earth, how long, how thick, and how broad it should be; he settled the borders and boundaries of it. This Job might know that the Lord did; but he laid them, and what they are that are laid, he knew not. Mathematicians pretend to give us the circumference and diameter of the earth; but in their accounts are not agreed, but widely differ; which shows they are at no certainty about them (e); and Job and the men of his age might be still less knowing: though the words may be rendered, "for thou knowest" (f); surely such a knowing man as thou art must needs know this and so are a severe sarcasm upon him;
or who hath stretched the line upon it? The measuring line being formed according to rule, with exact symmetry and proportion. This may be the same with the circle of the earth, and the compass set upon the face of the deep or terraqueous globe, Proverbs 8:27. And with the same exactness and just proportion are the ways and works of Providence, which Job ought to have acquiesced in as being well and wisely done.
(e) The mathematicians in Aristotle's time reckoned the breadth of the earth a little less than forty myriads of furlongs, and the length of it seventy myriads. Aristot. de Mundo, c. 3. Vid. Plin. Nat. Hist. l. 2. c. 108, 109. According to the moderns, the circumference of the earth is 25,031.5 of our statute miles, and its diameter 7967 such miles. See Chamber's Dictionary on the word "Earth". (f) "quadoquidem", Junius & Tremellius, Piscator; "quia", Michaelis; "nam", Schultens; so Broughton.

measures--of its proportions. Image from an architect's plans of a building.
line--of measurement (Isaiah 28:17). The earth is formed on an all-wise plan.

Measures - Who hath prescribed how long and broad and deep it should be. Line - the measuring line to regulate all its dimensions.