If you are using the ethnicity calculators at gedmatch, then it is taking your DNA and comparing it to the various populations that it has as a reference set. It gives output that is basically a 100% stacked bar graph. Those graphs show you at each SNP position which of those reference populations is most likely match your DNA.
Of course if your ancestry isn’t one of the reference populations, then it is little more than a guess, or maybe even worse than a guess.
I suggest you go to the ethnicity calculators, and check which reference populations make up the set for each. They should be listed.
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