Those numbers explain why power density matters so much: if you start with a source that has low power density, you have to compensate for that low density by utilizing more resources such as land, steel, and ultra-long transmission lines.

FORBES: Magazine Article

During the climax of the pilgrimage, crowds can reach a density of up to seven people every 10 square feet -- the perfect storm of flu transmission.

CNN: The Hajj: A perfect storm for swine flu?