They go up by the mountains; they go down by the valleys unto the place which Thou hast founded for them.
After God judged the earth and its inhabitants by flood waters (Genesis 7:18-20), the flood waters resented from parts of the earth to create the continents and islands of this world. God had a place established for them. Man would live upon the land.
Although this text is describing the world before the flood, water did cover everything again after the flood took place. Remember the flood was caused in part by the waters in the sky coming down on the earth. Waters in the ocean prior to the flood somehow sunk in the earth so that landmasses did appear. Those oceans cannot and never did rise again to a point where they could cover the world’s surface with water.
 Thou hast set a bound that they may not pass over; that they turn not again to cover the earth.
We ought to appreciate all God has done for us by making this world. He has appointed a boundary the waters could not transcend, so that they will never cover the earth again according to verse 9. This verse recalls the Lord’s covenant with Noah (Genesis 9:11) where He stated that He would never destroy the earth by flood again.