You can reduce two-dimensional space to one-dimensional space by assuming the two-dimensional space is shaped like a spiral, if we don’t have completeness in our number system. This is because any point, on an appropriate number-system, and on, say, a piece of paper, could be described by a single length.

For three dimensions it is also possible, if you imagine a spiral going around a sphere from top to bottom, widening as it circles the sphere, and then turning around and following the same pattern back up, etc, would make it possible to describe any point in 3-space with a single length.

Time is usually the one dimension that can describe everything, but space can be reduced to one dimension too.