THE incredible expansion of the world’s major cities has been highlighted in compelling images shot over the last three decades.

The maps, published by news.com.au for United Nations World Population Day, aims to highlight the importance of global population and the increasing demand for urban expansion.

The current world population sits at 7.6 billion, with China, India and the United States being the three most populous countries.

Australia sits at 54 on the list with 24.7 million people, but the national population is expected to hit 25 million this August, a milestone that wasn’t projected until 2051.

Descartes Labs, a predictive intelligence company, has tracked expansion in ‘megacities’ including Las Vegas and Beijing using before and after aerial shots.

Jason Schatz, applied scientist from Descartes Labs explained the images were captured using Landsat, which is a series of Earth observing satellites.

“Seeing snapshots of growth over 30 years is a really dramatic way to visualise local, regional, and global changes,” Mr Schatz said.

“The decades-long imagery archive from the Landsat program represents the only globally ubiquitous physical record of changes like these — every city on earth can be visualised the same way with the same instrument.”

Beijing, China

Since 1984, Beijing has grown from six million to 23 million and is still growing at a considerable rate. Mr Schatz said urban expansion in China is hard the fathom: “The growth of Beijing and Chongqing is matched or surpassed by dozens of cities across China, all of which have populations in the millions or tens of millions.”

Chongqing, China

ppearing almost out of nowhere to assist the migration of 1.3 million people, Chongqing didn’t formerly exist until 1997. As of 2015, Chongqing has 30 million and an urban population of 18.38 million.

Sao Paulo, Brazil

Sao Paulo’s expansion differs from other cities Descartes Labs decided to track. “Much of its growth was “up” rather than “out”, and was associated with a tremendous economic expansion that does not manifest as clearly in an expanded urban footprint.” Mr Schatz explains.

Dubai, United Arab Emirates

Population growth in Dubai continues to be one of the strongest in the world, having grown from 350,000 in 1984 to 2.7 million in 2017. Mr Schatz attributes the growth to the impressive expansion, “particularly the infrastructure and buildings over the water.”

Las Vegas, USA

Clark County of Las Vegas has grown from 500,000 people to 2.25 million since 1984. Due to the relatively young population, the county experiences more births than deaths, explaining the rapid population growth.

World Population Day is for global observation, aiming to draw attention to issues relating to the global population, such as the implications of population growth on the environment and development, gender equality, poverty, human rights and at the forefront this year, family planning.

The United Nations will be celebrating 50 years since the 1968 International Conference of Human Rights, where family planning was first acknowledged as a human right, hence this years theme: Family Planning is a Human Right.

The 1968 conference resulted in the Tehrean Proclamation, which stated “Parents have a basic human right to determine freely and responsibly the number and spacing of children.”

Editor's Note: This article was originally published in news.com.au on Sunday July 8th, 2018 http://bit.ly/Bigcities