This is an idiom that refers to traveling toward Jerusalem, which was on higher ground than the surrounding area. (See: [[rc://en/ta/man/translate/figs-idiom]])
"whom Nebuchadnezzar, ruler of Babylon, took away from their home country." The army of Babylon did this under the command of Nebuchadnezzar. (See: [[rc://en/ta/man/translate/figs-metonymy]])
A census had been taken when the Israelites first returned to Jerusalem after the exile. The numbers represent how many men belonged to each family group. This sentence introduces the information in the following verses.