The words "up and down" mean in every direction. Alternate translation: "the land in every direction" or "throughout the land" (See: [[rc://en/ta/man/jit/figs-idiom]])
The land that they are to survey is spoken of as if it were an inheritance that each of the tribes would receive as a permanent possession. (See: [[rc://en/ta/man/jit/figs-metaphor]])