I’ll get back to you on your blood-alcohol concentration.
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.