UNITED NATIONS — Yeonmi Park calls herself a former slave from North Korea. She had never seen a world map. She nearly starved. After she underwent appendix surgery without anesthesia at age 13, Ms. Park recalled, she saw human bodies piled outside the hospital, their eyes eaten by rats.

Convinced she would die in North Korea, Ms. Park said, she and her mother fled to China, where human traffickers sold her for $200. Two years later, after escaping by walking across the Gobi Desert into Mongolia, Ms. Park found refuge in South Korea. She has no idea what happened to her North Korean relatives, Ms. Park said.

“The scariest thing for me that night crossing the desert,” she said, “was being forgotten. No one knows that I existed in this world.”

Ms. Park, 24, now a student at Columbia University in New York, recalled her ordeal Thursday at a news conference held at the United Nations to publicize a new survey about modern slavery — a broad term used by rights activists that includes forced labor, forced marriage and sexual exploitation.