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The neutral hydrogen 21 cm line is an excellent tracer of the atomicinterstellar medium in the cold and the warm phases. Combined 21 cm emissionand absorption observations are very useful to study the properties of the gasover a wide range of density and temperature. In this work, we have used 21 cmabsorption spectra from recent interferometric surveys, along with thecorresponding emission spectra from earlier single dish surveys to study theproperties of the atomic gas in the Milky Way. In particular, we focus on acomparison of properties between lines of sight through the gas disk in theGalactic plane and high Galactic latitude lines of sight through more diffusegas. As expected, the analysis shows a lower average temperature for the gas inthe Galactic plane compared to that along the high latitude lines of sight. Thegas in the plane also has a higher molecular fraction, showing a sharptransition and flattening in the dust - gas correlation. On the other hand, theobserved correlation between 21 cm brightness temperature and optical depthindicates some intrinsic difference in spin temperature distribution and afraction of gas in the Galactic plane having intermediate optical depth (for0.02 < $\tau$ < 0.2) but higher spin temperature, compared to that of thediffuse gas at high latitude with the same optical depth. This may be due to asmall fraction of cold gas with slightly higher temperature and lower densitypresent on the Galactic plane.

Properties of atomic hydrogen gas in the Galactic plane from THOR 21-cm absorption spectra: a comparison with the high latitude gas