NASA's Landsat satellite system has been orbiting and taking pictures of the earth since 1972. In honor of its 40th birthday, NASA and the U.S. Geological Survey have released a cool set of images showing how 11 world cities have changed over that time. This site features two overlaid images of each city from different years dating back to the 1970s, with a cool slider bar to let you see how each city has changed. To make the drastic changes of time even more apparent, we've made some animated GIFs of those images.
Tokyo - 1989 and 2011
These false-color images of Tokyo show a very dense city becoming even more so. The green areas represent open or vegetated space, while the pinks and purples represent urbanized areas. Tokyo prefecture grew from a population of about 11.4 million in 1970 to more than 13 million in 2010. The metropolitan area grew by about 7 million people over that time, and now stands at nearly 37 million.
Ouagadougou, Burkina Faso - 1986 and 2006
In 2006, Ouagadougou was home to about 1.4 million, more than doubling its 1998 population of 690,000. Along with this growth has come a rapid spreading of the city's reaches. Again, the pink and purple tones show urbanized areas, and the expansion of the city between 1986 and 2006 is extensive in all directions.
Chicago area - 1985 and 2010
40 miles to the west of Chicago, these images show a quarter-century's worth of suburbanization.
Las Vegas - 1984 and 2011
There are two very stark things happening in this animation: the rapid development of Las Vegas into the desert and the dramatic reduction of water in the nearby Lake Mead* reservoir. The connection between the two should be obvious.
Tehran - 1985 and 2009
In 1986, Tehran's population was about 6 million. By 2009 it had grown to more than 10 million, and the city has spread out to accommodate this growth.
Chandler, Arizona - 1985 and 2011
The biggest of the suburban cities to develop in between Phoenix and Tucson, Chandler has seen explosive growth over the past few decades. The population was less than 50,000 until the early 1980s, but has since shot up to more than 230,000 as of the 2010 Census.
Istanbul - 1975 and 2011
As Istanbul goes from blood red to grayish-beige in these images, the population grows from about 2.5 million in 1975 to 13 million in 2011.
Ontario, California - 1985 and 2010
This southern California city has seen massive growth in recent decades. As can be seen in the lower left corner of these images, warehouse space has spread widely around the city's airport over the past quarter-century.
Dubai - 2000 and 2010
One of the best examples of the instant megacity, Dubai has changed dramatically since oil was discovered there in the 1960s. The change over just the past decade has been incredible.
Santiago, Chile - 1985 and 2010
In the early 1980s, Santiago's population was around 4 million. By 2010 it had reached nearly 5.8 million.
Pearl River Delta, China - 1973 and 2003
The starkest transition from rural to urban has taken place over just 30 years in the Pearl River Delta in southeastern China. Virtually overnight, megacities like Guangzhou and Dongguan have developed, and each now boast more than 12 and 8 million residents respectively.
*An earlier version of this article incorrectly referred to the reservoir outside of Las Vegas as Lake Powell.
Images courtesy NASA and USGS