"Iso" lines are lines on a map joining places of equal value: isohyets join equal rainfall, isobars join equal atmospheric pressure, and isotherms join equal temperature.
- "Iso" is Greek for "equal"; an isoline (or isopleth) connects points of the same value of some quantity on a map.
- Isohyet: a line joining places that receive equal amounts of rainfall over a period; used to map the distribution of precipitation.
- Isobar: a line joining places of equal atmospheric pressure (reduced to sea level); closely spaced isobars mean a steep pressure gradient and strong winds, and they define highs and lows on weather maps.
- Isotherm: a line joining places of equal temperature; isotherms generally run east-west (parallel to latitude) but bend over land and sea due to differential heating.
- Other examples include isohaline (equal salinity), isohel (equal sunshine), and contour lines (equal elevation), all built on the same principle.
The exact meaning of each "iso" line (rainfall, pressure, temperature) and the inference that close isobars mean strong winds are recurring climatology and map-reading facts.
Isohyet (rainfall), isobar (pressure), isotherm (temperature): keep the three apart. Closely spaced isobars indicate strong winds (steep pressure gradient), not calm conditions.
Equal-value map lines: isohyet (rainfall), isobar (pressure), isotherm (temperature); close isobars mean strong winds.