The article explores different ways to define the tropics and maps out where they are located on Earth. By using various criteria, the researchers found that the size of the tropics can vary greatly, from 23 million to 66 million square kilometers. They also discovered that only 44% of recent tropical biology studies were conducted in the core tropics, with some studies taking place in areas with tropical climates outside of the traditional tropics. This shows that there are inconsistencies in how tropical areas are classified and studied.