The correct answer is option 4, Isotherm. An isotherm is a line on a map that connects points of equal temperature at a given time. It is used to represent the distribution of temperature across a region or area. Each isotherm represents a specific temperature value, and the lines can vary in shape and spacing depending on the temperature gradient in the area. For example, if there is a sharp change in temperature over a short distance, the isotherms will be closely spaced together. On the other hand, if the temperature changes gradually over a larger area, the isotherms will be spaced farther apart. Isotherms are commonly used in meteorology and climatology to analyze and predict weather patterns and climate conditions.