Full & Empty of People

Population density (in agriculture standing stock and standing crop) is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans. It is a key geographic term. Population density is population divided by total land area.

Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect after the scientist who identified it. Different species have different expected densities.

For humans, population density is the number of people per unit of area usually per square kilometer or mile (which may include or exclude cultivated or potentially productive area). Commonly this may be calculated for a county, city, country, another territory, or the entire world.

The world's population is 6.8 billion, and Earth's total area (including land and water) is 510 million square kilometers (197 million square miles). Therefore the worldwide human population density is 6.8 billion ÷ 510 million = 13.3 per km² (34.5 per sq. mile). If only the Earth's land area of 150 million km² (58 million sq. miles) is taken into account, then human population density increases to 45.3 per km² (117.2 per sq. mile). Several of the most densely-populated territories in the world are city-states, microstates, micronations, or dependencies. These territories share a relatively small area and a high urbanization level, with an economically specialized city population drawing also on rural resources outside the area, illustrating the difference between high population density and overpopulation.

http://en.wikipedia.org/wiki/Population_density

come and go

Someday were full of people

Persepolis (Old Persian Pārsa, Takht-e Jamshid or Chehel Minar) was the ceremonial capital of the Achaemenid Empire (ca. 550-330 BCE). Persepolis is situated 70 km northeast of the modern city of Shiraz in the Fars Province of modern Iran.

Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, its sister city, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning two days in 79 AD.

      
Some are ;
 Full of every possible thing but absolutley not people!

But at the same time

There are some places that now are full of people

New York is the most populous city in the United States, and the center of the New York metropolitan area, which is one of the most populous metropolitan areas in the world. A leading global city, New York exerts a powerful influence over global commerce, finance, media, culture, art, fashion, research, education, and entertainment. As host of the United Nations Headquarters, it is also an important center for international affairs. The city is often referred to as New York City or the City of New York to distinguish it from the state of New York, of which it is a part.


Located on a large natural harbor on the Atlantic coast of the Northeastern United States, the city consists of five boroughs: The Bronx, Brooklyn, Manhattan, Queens, and Staten Island. The city's 2009 estimated population approached 8.4 million, and with a land area of 305 square miles (790 km²), New York City is the most densely populated major city in the United States.

The New York metropolitan area's population is also the nation's largest, estimated at 19.1 million people over 6,720 square miles (17,400 km²). Furthermore, the Combined Statistical Area containing the greater New York metropolitan area contained 22.2 million people as of 2009 Census estimates, also the largest in the United States.

New York was founded as a commercial trading post by the Dutch in 1624. The settlement was called New Amsterdam until 1664 when the colony came under English control.New York served as the capital of the United States from 1785 until 1790. It has been the country's largest city since 1790. As many as 800 languages are spoken in New York City, making it the most linguistically diverse city in the world.

 

http://en.wikipedia.org/wiki/Perspolis

http://en.wikipedia.org/wiki/Pompeii

http://en.wikipedia.org/wiki/New_York_City