Who was Dr. Jonas Salk?

Jonas Edward Salk was an American virologist and medical researcher who developed one of the first successful polio vaccines.

Salk, born in New York City in 1914, first conducted research on viruses in the 1930s when he was a medical student at New York University, and during World War II helped develop flu vaccines.

map scale refers to the relationship (or ratio) between distance on a map and the corresponding distance on the ground. for example, on a 1: 100000 scale map, 1cm on the map equals 1km on the ground.