We may distinguish cities in our minds based on landmarks, the people that live there, or other factors — but science may have found a new, important way to tell cities apart.

As it turns out, every city has its very own germ signature, according to an American Society for Microbiology statement.

Researchers were trying to figure out how to measure microbes in an office, but instead discovered that they could tell germs apart simply by what city they were taken from.

It didn’t appear to matter if the officers were totally different from one another, they still had the same basic microbe signature if they were in the same city, the research team found. It’s a fascinating finding because offices even in the same city have different usage patterns, ventilation systems, and sizes. Despite all this, geography was the biggest factor in what germs were found.

They also found that the microbes don’t change much from one year to the next.

The researchers were looking for the best materials for germ tests when they made the discovery. They had set some germ-gathering materials in offices in locations as varied as San Diego, Toronto, and Flagstaff, Ariz.

“We suspect that in the absence of extreme conditions like flooding, microbes may be passively accumulating on surfaces in the built environment rather than undergoing an active process,” senior study author J. Gregory Caporaso, PhD, an assistant professor of biological sciences and assistant director of the Center for Microbial Genetics and Genomics at the university, said in the statement. “As we continue to expand our understanding of the microbiology of the built environment, possibly including routine monitoring of microbial communities to track changes that may impact human health, our results will help inform future research efforts.”

The findings were “especially interesting because even within each city, the offices we studied differed from each other in terms of size, usage patterns, and ventilation systems,” he added, “suggesting that geography is more important than any of these features in driving the bacterial community composition of the offices within the ranges that we studied.”