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A 3D surface map of Mt. St. Helens with a 2D contour map above for comparison. In mathematics, geology, and cartography, a surface map is a 2D perspective representation of a 3-dimensional surface. [1] Surface maps usually represent real-world entities such as landforms or the surfaces of objects.
An isobar (from Ancient Greek βάρος (baros) '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.
Typical applications include the contour lines on topographic maps or the generation of isobars for weather maps. Marching squares takes a similar approach to the 3D marching cubes algorithm: Process each cell in the grid independently. Calculate a cell index using comparisons of the contour level(s) with the data values at the cell corners.
Such maps have been in use since the mid-19th century and are used for research and weather forecasting purposes. Maps using isotherms show temperature gradients, [2] which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, [3] on a constant pressure surface of 300 or 250 hPa show where the jet stream is located.
Contour line (line of constant elevation or depth, sometimes used to describe other lines of constant value) A line of constant value on a map or chart. Examples include isobar (equal barometric pressure), isotherm (equal temperature), and isohyet (equal precipitation). Isoline, an opera by André Messager
Isopachs are contour lines of equal thickness over an area. Isopach maps are utilized in hydrographic survey, stratigraphy, sedimentology, structural geology, petroleum geology and volcanology. An isopach map is similar to an isochore map, but these terms actually describe different methods of displaying thickness variations within a layer. [1] [2]
Once a map has a field of station models plotted, the analyzing isobars (lines of equal pressure), isallobars (lines of equal pressure change), isotherms (lines of equal temperature), and isotachs (lines of equal wind speed) are drawn. [18] The abstract weather symbols were devised to take up the least room possible on weather maps. [citation ...
On weather maps, high-pressure centers are associated with the letter H in English, [16] or A in Spanish, [17] because alta is the Spanish word for high, within the isobar with the highest pressure value. On constant pressure upper level charts, it is located within the highest height line contour. [18]