Isotherms

(i) They are imaginary lines drawn on the map joining places hav­ing the same temperature when reduced to sea level.

(ii) Closely spaced isotherms indi­cate great range of temperature.

(iii) The unit of measurement is de­gree (°C) Celsius or Fahrenheit.

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Isobars

(i) They are imaginary lines drawn on the map joining places hav­ing the same atmospheric pres­sure when reduced to sea level.

(ii) Close spacing of the isobars means steep rise/fall in pressure.

(iii) The unit of measurement is in millibars (mb).