An isometric line is an imaginary line in a three-dimensional space, where the direction of the line is neither parallel nor perpendicular to any of the axes. Synonyms for isometric line include isopleth, isogram, contour line, and isochron. Isopleth is used more commonly in meteorology and geology, referring to lines of equal values of a specific measurement, such as temperature or pressure. Isogram refers to lines on a map that connect points of equal value, often used in cartography. Contour line indicates lines that join points of equal elevation on a topographic map. Isochron is used in geology to denote a line on a map that connects points of equal geological age.