It's an interesting question. What is nationality? A definition from WikiPedia is "A nation is a group of people who share culture, ethnic origin and language.".
Exploring this theme yields little benefit in Scotland, the language of the average Weedie is subtly different from my own Perthshire origins. While we all nominally speak english, I was raised with a smattering of the Doric to add spice to my already enriched English lexicon; whereas the West coast Glasgow dialect has its own unique sounds and words. Then we have the Islanders who cling to the Gaelic in part, linguistally entirely separate from us.
Ethnic origin? Interesting again, it is clear that the average height in Glasgow and the West coast is smaller than in Aberdeen and the North East. In terms of ethnic origin the Weediges clearly came from the Scots invasion from Eire, while the Furry Boots obviously retain some of the Pictish with touches of Viking.
Culture? Well I am partial to a twa holer bridie and the occasional ootsider, while my Weedgie South Side chum has a roll and sausage with a bottle of ginger. I'll have a dram or four, while he will savour a glass of chilled Buckfast (maybe thats an age thing).
I do know that my Weedige colleague, my Hebridean sister-in-law and my Ochil's friends are all one thing - Scottish (including the ones born by accident of birth outside this fine land). What I don't know is how to define it. Any suggestions?