Before a megaproject gets the nod to go ahead, a very unique set of circumstances must first be considered.
There is no blueprint or shortcut for building a world-changing megaproject. In fact, each one must be designed and built from the ground up, often amidst considerable amounts of red tape and criticism. Builders of megaprojects embrace the unknown, even when faced with incredible amounts of risk and massive cost overruns.
At the same time, successful megaprojects can accomplish things that have never been done before. They can be pinnacles of human achievement, and spectacles such as the International Space Station and the U.S. Interstate Highway System have already changed the world.
This infographic from Futurism details nine of the world's largest megaprojects currently in construction.
They range from giant $64 billion theme parks (Dubailand) to massive canals that will take 48 years to build (South-North Water Transfer Project in China).
Here are the nine largest megaprojects in construction right now, in order from most to least expensive:
1. International Space Station - $150 billion (as of 2010)The most expensive single item ever built. Expansions beyond 2020 are estimated to eventually cost $1 trillion.
2. Al Maktoum International Airport - $82 billionThis airport in Dubai will be fully operational by 2018. It will be the world's largest in terms of size and passenger volume - so big that four jets will be able to land simultaneously.
3. South-to-North Water Transfer Project - $78 billion (as of 2014)Thought the Three Gorges Dam was massive? This other Chinese megaproject is already nearly three times as expensive - it aims to divert water from the Yangtze River using three huge canals to bring it to the north of the country.
4. California High-Speed Rail - $70 billionSpanning 1,300 km (808 mi), this will link San Francisco to Los Angeles.
5. Dubailand - $64 billionThis mega theme park project will open in 2025 in Dubai. It will also have the world's largest hotel (6,500 rooms), sports venues, eco-tourism, science attractions, and a giant mall.
6. London Crossrail Project - $23 billionLondon is expanding its underground system, with 42 km (26 mi) of new tunnels to connect 40 stations. Everything will be complete by 2020.
7. Beijing Daxing International Airport - $13 billionOpening in 2025, this airport megaproject will have seven runways and the largest terminal in the world. It will help ease the load on nearby Beijing Capital International Airport.
8. Jubail II - $11 billionThe second phase of development of the Jubail Industrial City in Saudi Arabia will add 100 industrial plants, an oil refinery, and one of the bigger desalination plants in the world.
9. Hong Kong-Zhuhai-Macao Bridge - $10.6 billionA series of bridges and undersea tunnels to link the three major cities on the Pearl River Delta in China. Ultimately, it will be 50 km (31 mi) of links, opening sometime beyond 2021.