The degree of human thickness in the area will show the amount of people. Higher degrees of human thickness = more people. Lower degrees of human thickness = less people. That is the population density of the area, or the concentration of people.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
I’ll get back to you on your blood-alcohol concentration.