Ok, I originally thought that 'Mediterraneans' were dark-skinned people from the Mediterranean and Middle East, that the 'Nordics' were blond-haired blue-eyed people from the Germanic world and that the 'Alpine' people were people from the rest of Europe who didn't look quite as Scandinavian as the Nordics. But I've seen maps where the Celtic peoples of Wales and Ireland were considered 'Mediterranean', and where Tajiks were considered to be 'Alpine'.
So, what exactly was the logic behind those three categories? Was it just completely subjective and defined by pure prejudice? And also, which of the 3 sub-races would people from the North of India or the Horn of Africa have been classified as?
It seems like you are asking about a specific classification system that I am unfamiliar with, so I can't answer as the logic behind it. I can however say that it isn't based on any modern understanding of "race", which is emphatically not a biological category (see the AAA statement on race). As such, making distinctions between "Nordic", "Alpine", and "Mediterranean" based on physical features is a bit of a folly. Certainly, people living in certain geographic ranges tend to share some certain physiological features (such as hair color, say) but these not at all hard and fast categories, and especially not categories analogous to a "race".
With the vast expansion of scientific knowledge in this century, however, it has become clear that human populations are not unambiguous, clearly demarcated, biologically distinct groups. Evidence from the analysis of genetics (e.g., DNA) indicates that most physical variation, about 94%, lies within so-called racial groups. Conventional geographic "racial" groupings differ from one another only in about 6% of their genes. This means that there is greater variation within "racial" groups than between them. In neighboring populations there is much overlapping of genes and their phenotypic (physical) expressions.
Emphasis mine. Any sort of categorization based on physical characteristics is bound to have the kind of ambiguity you are talking about precisely because human populations defy that easy of a characterization based on physical traits. Those categories are going to be messy because human physical traits are likewise messy.
If you can be more specific about where you encountered these categories, you might be able to receive a more specific and helpful answer.