What is a reference panel?

A reference panel is a set of people whose DNA is typical of DNA from a certain place or group.  

When you take an AncestryDNA test, we compare your DNA to the DNA in our reference panels to identify your ancestral origins. For example, to determine your ancestral regions, we find the reference panel DNA that's most similar to each segment of your DNA. Then, we assign your segments to the regions they resemble. So, if a piece of DNA is most similar to the reference panel DNA from Tonga, that segment will go into the "Tonga" bucket. 

The reference panel for our ancestral regions has 295,000 DNA samples that divide the world into 302 overlapping regions and groups.