The Isotherm Line, which divides the India North-South into almost two equal parts in the month of January is 20°C. Isotherms are the lines that connect points of equal temperature on weather maps, so at every point along a given isotherm, the temperature values are the same. Isotherms help to visualize and to interpret the horizontal temperature distribution of an area by showing the patterns of temperature on a weather or oceanography map. Constructing the map of isotherms is an elementary step in the temperature data analysis, and the process, in general, is known as contouring. It can even be done for the other parameters like barometric pressure (isobars), dew point temperature (isodrosotherms), geopotential height (isohypses), wind speed (isotachs), and salinity (isohalines). Isotherms are always smooth, labelled with the values, and mostly parallel to each other.