Isograms
Isograms
(also isolines), lines of equal value of some magnitude in its distribution on a surface, in particular on a plane (geographic map, vertical cross section, or graph). Isograms reflect continuous change in the quantity under investigation as a function of two other variables, for example, of geographic latitude and longitude on maps. Table 1 lists some isograms.
Isograms on maps are used most extensivey to characterize the values of continuous quantities and quantities that change gradually in space (for example, air temperature). However, they also perform much more varied functions. They are used on maps to indicate change in the quantitative characteristics of phenomena with time (for example, secular changes in the components of the earth’s magnetism), the rate of change of phenomena (for example, wind velocity), the time of occurrence of certain phenomena (for example, the onset of the first autumn frosts), the duration of phenomena (for example, the number of days with snow cover), the orientation of some physical quantities (for example, magnetic declination), and the frequency or probability of phenomena (for example, the frequency of thunderstorms). If at least one of the independent variables is some quantity other than a geographic coordinate, then the isograms are called isopleths.
IU. G. KEL’NER
| Table 1. The most common isograms | ||
|---|---|---|
| 1 The part of the term after the prefix is of Greek origin unless otherwise indicated | ||
| Name | Etymology1 | Phenomenonbeing described |
| Hydroisobath | bathos, “depth” | Depth of groundwater table relative to earth’s surface |
| Hydroisohypse | hypsos, “height” | Elevation of groundwater table above sea level |
| Hydroisopiesos | piezo, “I press” | Pressure of artesian waters |
| Isallobars | bams, “weight” | Change in atmospheric pressure per unit time |
| Isallohypse | hypsos, “height” | Change in elevation of isobaric surface per unit time |
| Isallotherm (isoallotherm) | therme, “heat” | Change in air temperature per unit time |
| Isametral | ametros, “incommensurable,” “irregular” | Same as isanomal |
| Isamplitudes (isoamplitudes) | Latin amplitudo, “magnitude” | Amplitude of change in meteorological elements over some interval of time. |
| Isanemone (isovel) | anemos, “wind” | Average wind velocity over some period of time |
| Isanomal (isametral) | anomalos, “irregular” | Deviation of some quantity (temperature, amount of precipation) from value adopted as norm (average long-term, average latitudinal) |
| Isoantho | anthos, “flower,” “blossoming” | Times when certain plants blossom |
| Isoatmosphere | atmos, “vapor,” “evaporation” | Magnitude of evaporation or evaporability for a certain time interval |
| Isobase | basis, “stepping,” “base” ana, “upward” cata, “downward” | Magnitude of tectonic movements (uplifts— isanabases–or subs- idences—isocatabases) over some interval of time |
| Isobar | baros, “weight” | Atmospheric pressure |
| Isobath | bathos, “depth” | Depth of bodies of water |
| Isobront | bronte, “thunder” | Number of days with thunderstorms |
| Isochrone | chronos, “time” | Times of occurrence of some phenomenon |
| Isoclinic line | klino, “I lean” | Magnitude of magnetic clip |
| Isodynamic line | dynamis, “force” | Full intensity of the earth’s magnetic field or its components |
| Isogonic line | gonia, “angle” | Orientation of certain physical quantities (magnetic declination, wind direction) |
| Isohaline | hals, “salt” | Salinity of waters |
| Isohion | chion, “snow,” “snow cover” | Thickness or duration of snow cover |
| Isohyet | hyetos, “rain” | Amount of precipitation in a certain period |
| Isohypse (horizontal) | hypsos, “height” | Elevation of the earth’s surface above sea level |
| Isoneph | nephos, “cloud” | Cloudiness |
| Isopach | pachys, “thick,” “massive” | Thickness of geological strata of certain age or composition |
| Isophase | Greatest phases of solar eclipse | |
| Isophene | phaino, “I show” | Times or duration of certain phenological phases |
| Isopor | poms, “path,” “passage” | Secular changes in components of earth’s magnetism |
| Isorhachic line | rhachia, “surf,” “ocean waves” | Elevation of ocean tides |
| Isoseismal | seistos, “set to oscillat-ing,” “oscillated” | Intensity of earthquakes |
| Isotac | teko, “I melt” | Times when frozen inland waters thaw |
| Isotach | tachos, “speed” | Velocity of currents |
| Isotherm | therme, “heat” | Temperature of air, water, and soil |
| Isothermobath | therme, “heat” bathos, “depth” | Water temperature in the depths of bodies of water |
| Isovel | Latin velox, “quick” | Same as isanemone |