Tools in this 4D (x-y-v-Intensity) Space
Speedometers: v(z) gives gas velocity
Tachometers: v(z)[(x,y)] measures angular momentum
Thermometers: chemical analyses & line strength inter-comparison give Tex, Tkinetic
Pseudo-thermometers: line widths give velocity dispersion (usually >> sound speed)
Magnetometers: Zeeman Effect & polarized spectral-lines give B
Combinations give density, mass