There are many ways to do this: https://en.wikipedia.org/wiki/Complex-base_system https://en.wikipedia.org/wiki/Complex-base_system But it seems clear that the

There are many ways to do this: https://en.wikipedia.org/wiki/Complex-base_system https://en.wikipedia.org/wiki/Complex-base_system But it seems clear that the grandparent poster was using the wrong word (“digit”) and likely meant something like “we can conceive of a 2-dimensional quantity as a single number-like entity”.