Contour line factors in a weather system. An isobar (from or "baros", meaning 'weight') is a line of equal or constant pressure on a graph, plot, or map; an isopleth or contour line of pressure. More accurately, isobars are lines drawn on a map joining places of equal average atmospheric pressure reduced to sea level for a specified period of time. In meteorology, the barometric pressures shown are reduced to sea level, not the surface pressures at the map locations. The distribution of isobars is closely related to the magnitude and direction of the wind field, and can be used to predict
Contour line isotherms in Paris, in 1817. An isogeotherm is a line of equal mean annual temperature. An isocheim is a line of equal mean winter temperature, and an isothere is a line of equal mean summer temperature. An isohel (from or "helios", meaning 'Sun') is a line of equal or constant solar radiation. An isohyet or isohyetal line (from or "huetos", meaning 'rain') is a line joining points of equal rainfall on a map in a given period . A map with isohyets is called an isohyetal map. An isohume is a line of constant relative humidity, while a isodrosotherm (from