There is a physical discontinuity between, say, California and Hawaii, or the Australian mainland and Tasmania. But there are other phenomena where the discontinuity between them does not lie in nature, but rather in culture. California vs Nevada, Queensland vs New South Wales, etc. There the line is drawn by humans for historical and political reasons. These are the lines you see on political rather than physiographic maps.
Psychiatric nosology is like a political map.
There are, so far, no demonstrable discontinuities in nature to underpin the different conditions and the boundaries between them. There are, of course, other ways of defining them, just as there is for the equator. When it comes to dealing with the essence of a condition, this probably doesn't matter. Whether it is core depression, core panic, or core trauma reaction. But when one is adjudicating whether an individual person lies one side of a boundary or the other, it is quite important to understand what sort of boundary one is talking about.