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 after it circles the sphere and turns around following a similar pattern back up, etc. It is 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.