Is it possible for a city full of people to be clean and green - and to look after the well-being of its citizens by design?
That's the hope behind two separate projects in the works in China and Malaysia.
The Malaysian government has announced plans to build a green mega-city called Iskandar Malaysia. And it's going to be huge.
The city is expected to be the size of Luxembourg - about 2,500 square kilometres - and house 3 million people by the year 2025.
It's being called an ultra-modern "smart metropolis," where energy is produced from renewable sources, transport will be publicly provided, and waste will be diverted to other uses.
The city's plan is also supposed to encourage social integration and mental well-being. It will feature green spaces and areas where people can relax and mingle, as well as a mixture of skyscrapers and low-rise buildings throughout, rather than separate business and residential districts.
And while the city is intended to help with Malaysia's expected population growth in the coming decades, it's also meant to be an example for other countries in the region to follow.
Future population growth in south-east Asia is expected to be mainly concentrated in cities. If this city model succeeds, it could create a higher standard of living for the people who live there.
Malaysia's prime minister Najib Razak said in a speech, "Iskandar Malaysia [is] a smart city template - protecting the environment, promoting equitable development and addressing urban development challenges..."
Meanwhile, China has also announced plans to build an eco-friendly city from scratch. 78 million square feet of land outside of Chengdu in central China has been chosen as the site of a city meant to house 80,000 people.
The 'Great City' will limit the environmental impact of its residents by promoting public transportation over traditional car use, producing clean energy, and reducing waste.
According to Adrian Smith + Gordon Gill Architecture, the firm behind the plans, it will be a city where "cars will be essentially unnecessary," although there will still be standard roads.
Half the road space will be reserved for non-motorized traffic, though, and electric shuttles will transport people to places they can't reach by walking. And every single home will be within a two-minute walk of a public park.
The planners claim that the city will use 48 per cent less energy and 58 per cent less water, and generate 89 per cent less waste, than a conventional development with a similar population.
Like Iskandar Malaysia, the plans are also supposed to encourage a thriving civic life, with affordable housing, education and medical care all clustered in the city centre.
Both of these cities sound like great ideas in principle: giving people an eco-friendly environment and safe, community-minded living spaces at the same time, while correcting some of the inefficiencies of traditional cities.
But as the Guardian pointed out back in 2009, similar projects have been promised in the past and failed to materialize.
Dongtan is the name of a proposed eco-city on Chongming Island in Shanghai. It was meant to be completed by 2010, in time for the Shanghai World Expo. Here's one of the concept images:
The idea for the city sounds great on paper: all the buildings were going to be zero-energy structures, meaning they would generate their own power. Gardens and other vegetation on rooftops would provide insulation and filter rainwater, and windows would have thermal glass to reduce the need for heating.
But by the time the Expo happened, none of the city had actually been built. And it still hasn't been.
Today, the area boasts 10 wind turbines, but no buildings, water taxis, water cleaning plant or energy centres, all of which are in the city plans. This is what it looks like now:
And there are also questions about whether building Dongtan is a sustainable choice.
The land that Dongtan is supposed to be built on is part of a shrinking green area outside Shanghai, and it's currently one of China's largest bird reserves.
According to a post on the Danish Architecture Centre site, the most sustainable use of the land would be to leave it alone.