The most affluent, Hartford, has among the lowest urban population densities in the world.
FORBES: Megacities And The Density Delusion: Why More People Doesn't Equal More Wealth
One remarkable similarity in all the fastest-growing areas is their relatively low population densities.
In the hyper-crowded skyscraper districts of Shanghai, densities can approach 125, 000 people per square mile.
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In large parts of America, where population densities are lower, it would be much costlier.
This kind of microscopic punched card reader and writer, is achieving fantastic data densities.
"Other approaches have proven reliability and similar speeds and the same or higher densities, " he says.
Densities are measured on a persons-per-square-mile basis and are rounded up to the nearest whole person.
There are many thriving American urban areas with densities below the U.S. average for large urban areas.
FORBES: Megacities And The Density Delusion: Why More People Doesn't Equal More Wealth
According to the UN, Addis has one of the higher densities of slum dwellers in the world.
It is hoped that building more compactly will increase population densities in cities that have been losing people.
"We hope to look at the densities of the krill that the penguins are exploiting, " Dr Trathan explained.
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"This is a very exciting development which demonstrates that high power densities are achievable by such innovations, " he said.
Much recent housing has been built to very low densities exacerbating urban sprawl.
Oxygen densities in both buildings were about 21%, high enough for workers to enter the buildings, the firm said.
Scientists have known for some time that large swathes of the earth's oceans harbor extremely low densities of phytoplankton.
The NVIDIA GRID technology is the best that we have seen for delivering high densities of HD-quality game streams to subscribers.
ENGADGET: NVIDIA details the Grid, a card built for powering cloud computing
Some papers at the conference projected that HAMR recording could take magnetic recording densities to perhaps 6 Tb per square inch (Tbpsi).
These particles boost storage densities to as high as 150 gigabits per square inch from the current standard of 35 gigabits per square inch.
Housing densities tend to be much lower in and around London than in other cities of similar scale like New York, Paris and Tokyo.
In 2010 the Australian government endorsed a control plan, the Australian Feral Camel Management Project, which aimed to reduce camel densities through culling and mustering the animals for sale.
However, the uncommon "tall sea pen" was found to be widespread, with high population densities present in the inner basins of Loch Broom and Little Loch Broom.
Attempts to encourage higher housing densities have been widely resisted.
The islands, lying between the Antarctic and Subtropical Convergences and the seas, have a high level of productivity, biodiversity, wildlife population densities and endemism among birds, plants and invertebrates.
This is because the country is spoilt with a long coastline and an abundance of mountains, valleys, rivers and rolling farmlands, plus one of the lowest population densities in Europe.
The inner two appear, from their densities, to have a lot of water or methane or ammonia in them (or any mixture of the three), along with hydrogen and helium.
The clouded leopard, the largest predator on Borneo, appears to live at very low densities within the reserve, as it has only rarely been photographed by the researchers or camera traps.
BBC: Earth News - Clouded leopard: First film of new Asia big cat species
In these places, construction is held back by slow-growing (Providence, Long Island) or declining (Detroit) populations or by already-high densities and building restrictions that leave fewer options for new construction (Orange County, CA).
While countries such as Bangladesh started micro-credit programmes in the 1970s, low population densities in many areas of rural Latin America have meant that micro-credit schemes have been seen as economically unviable in the region.
Moore's Law (which predicts that switch densities on silicon chips will double every 18 months, thus yielding a performance-doubling every 24 months) guarantees a 50 gigahertz chip in a Gateway or Dell box by 2010.
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