Map climatic features as the long-term mean values (of atmospheric pressure, temperature, humidity, total precipitation, and so forth) to connect points with equal values of the feature in question—for example, isobars for pressure, isotherms for temperature, and isohyets for precipitation. Isoamplitudes are drawn on maps of amplitudes (for example, annual amplitudes of air temperature—that is, the differences between the mean temperatures of the warmest and coldest month). Isanomals are drawn on maps of anomalies (for example, deviations of the mean temperature of each place from the mean temperature of the entire latitudinal zone). Isolines of frequency are drawn on maps showing
Atmospheric pressure m is the maximum height to which water can be raised using suction under standard atmospheric conditions. Low pressures such as natural gas lines are sometimes specified in inches of water, typically written as "w.c." (water column) gauge or "w.g." (inches water gauge). A typical gas-using residential appliance in the US is rated for a maximum of 14 w.g., which is approximately 1048.37hPa. Similar metric units with a wide variety of names and notation based on millimetres, centimetres or metres are now less commonly used. Pure water boils at at earth's standard atmospheric pressure. The boiling point is the temperature