This aerial view of Siem Reap, Cambodia, shows the West Baray reservoir (in black), 5 miles long by 1.5 miles wide, after a monsoon flooded the city in November 2002. The temple complexes of Angkor Wat and Angkor Thom are the square shapes directly to the right of the reservoir.
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Become A MemberEDITOR’S NOTE: The following maps and text are excerpted from “City Unseen: New Visions of an Urban Planet,” by Karen C. Seto and Meredith Reba, published by Yale University Press. The book collects satellite images of 100 cities that show, in colorful detail, the fragile relationship between Earth and its ever-expanding urban landscapes. The unexpected colors in the images are a recreation of light outside the visible spectrum in colors our eyes can see. Satellite sensors extend our vision into these frequencies and allow us to see the health of vegetation and the distribution of heat across a city, as well as urban attributes such as the types of materials used in buildings and roads. The excerpt reproduced here, “Plans,” celebrates the creativity and (sometimes unrealized) aspirations of different city visions.
Cities are the most visible and long-lasting human imprint on the land. How and where we build cities matters for the residents, for the environment, and for global sustainability. Modification of Earth’s surface through urban development is fundamentally changing the way living organisms and systems interact with each other and our planet. Urbanization transforms landscapes — from vegetated surfaces to buildings, pavement, sidewalks, and other artificial impervious surfaces. Cities themselves transform natural habitats. They break up habitats and transform local climates, rivers, water bodies, and air quality. The use of irrigation and major water diversion projects have allowed urban settlements to grow to immense sizes. From the design of neighborhoods and street layout, how and where urban areas develop affects resource use, biodiversity, human health, social cohesion, and ultimately, sustainability.
The impact of cities on the environment has expanded from local to global. As we move toward an urban century, a critical question is: What forms of urbanization are most environmentally and socially sustainable? Which forms of urban development promote stronger, more vibrant communities? What are the consequences of different patterns of urban development? What urban forms minimize use of resources such as water, energy, concrete, steel, and other raw materials? What are the social trade-offs of three billion new urban dwellers living in megacities of 10 million rather than in small cities?
Every great city starts with a vision. For centuries, urban or town planning has been a principal means to organize, structure, and standardize infrastructure, dwellings, and life within a city. Street design, city walls, and urban layouts have been developed for military purposes, to safeguard security, and to protect against invasion. Over time, street configurations, grid plans, and zoning emerged as central methods to limit access to roads and neighborhoods and to protect residents from vehicles or fast-moving traffic, or simply to reduce the amount of vehicular movement near residential zones.
Whereas historically, cities were places where housing and commerce were tightly woven and closely located, today many cities are zoned for single uses, leading to the separation of places of employment from places of residence. There is growing recognition that many tenets of twentieth-century urban planning and zoning have led to high consumption levels of land, water, and fossil fuels, affecting energy and climate systems worldwide.
Urban growth patterns evident in the United States during the second half of the twentieth century have now been adopted by many Asian developing nations. While the spread of American-style single-family detached homes in the suburbs is one relatively small dimension of urban expansion in the early twenty-first century, the environmental impacts of this trend appear to be of a proportionately greater significance because of the per-capita energy and land consumption required to sustain low-density development. If the built environment of the urban United States contributes to the country’s rank as the world’s most significant polluter, then the adaptation of similar built environments in nations with much larger populations presents a pressing environmental problem. New ideas about urban planning are critical to create healthier, more sustainable cities for the future.
Planned in 1957, Cape Coral, Florida, is shaped by an extensive canal system creating just under 400 miles (about 640 kilometers) of artificial coastline as the water flows through this interconnected waterway. Forcing water to flow through this extended waterway has affected tidal water levels, since ebbing and flowing water now must travel through this canal network. The Yucca Pens Unit State Wildlife Management Area, which sits north of the city (brown), is protected for hunting, fishing, and frogging.
Constructed in 1593 by the Venetians, Palmanova features a nine-pointed “star fort” or trace italienne — a defense system and geometric wonder. Six roads radiate from a hexagonal piazza at the center, with three leading to city gates and three to ramparts. Four ring roads link these radial roads. The whole fortress is surrounded by a moat, and the main buildings inside the fortress face the piazza. Despite its protected structure, no actual battles occurred in the fortress. People were reluctant to inhabit the fortress once it was completed, and it was later used as a residence for exonerated criminals. Today, about five thousand people live in the fortress, which is a national monument.
Designed by renowned urban planner and architect Le Corbusier in 1950 to have an ordered, grid street network, Chandigarh, located at the foothills of the Himalayas, was the first planned city in India after independence in 1947. The structured linear street network and large reinforced concrete buildings are atypical for Indian cities. The structure of the city has been likened to a living human body, with streets serving as “blood vessels,” homes as “cells,” and cars and people as “blood.”
Influenced by the work of Swiss-French urban planner Le Corbusier, the architect Lúcio Costa won a design competition for the new capital of Brasília, which was built between 1956 and 1960 to represent a new, more equitable capital in the interior of Brazil. It has been criticized for its large-scale design, which is car-dependent and is often cited as missing a sense of place. The city plan is also critiqued for its lack of mixed-use zoning, which integrates different land use types such as residential, commercial, industrial, and cultural. The bird’s-eye view of the city is often compared to the blueprint of an airplane, with the residential and commercial sections of the city spread out like wings from the main “fuselage” made up of the Eixo Monumental (Monumental Axis) and its iconic grand administrative structures.
Heralded as South America’s first planned city and a turning point in Argentinian urban planning, La Plata was designed by engineer Pedro Benoit in the form of a perfect thirty-six-by-thirty-six block square grid with a gothic cathedral at the city’s center and city squares or roundabouts at major intersections every six blocks. Diagonal boulevards transect the space to create a unique star-shaped pattern from above—especially at night since La Plata was the first urban street grid in Latin America to use electric street lighting.
An important cultural, religious, archaeological, architectural, and artistic center, Siem Reap spreads over 400 square kilometers (about 155 square miles) and is the gateway to the archaeological sites of Angkor, the center of the Khmer Kingdom (802 CE–1432 CE). It’s home to extensive stone temples and waterways including canals, dikes, and reservoirs, such as the West Baray — a reservoir 5 miles (8 kilometers) long by 1.5 miles (2.4 kilometers) wide with an average depth of 13 feet (4 meters), pictured in the center of the image. It is the largest human-made lake of the Khmer civilization and was thought to originally have been filled by rainwater, although today a series of channels and moats leads to the water body. In this image, captured in February 2004, we see the low-water level in the baray as the deep blue fades into red. February is one of the driest months of the year, evidenced by sparser vegetation (red) in the bottom image.
The word eixample means expansion or extension in Catalan, and the Eixample district was conceived in the mid-1800s in response to Barcelona’s high rates of morbidity and mortality. The district’s orderly chamfered octagonal blocks with wide boulevards and airy sunlit courtyards are in stark contrast to the dense labyrinth of narrow streets of the older city, located in the top part of the image.
Based on the principles of the kibbutz such as communal ownership of land, equality, and social justice, while still allowing for private ownership of land, Nahalal was developed by architect Richard Kaufmann in 1921 as a cooperative agricultural settlement. In a layout resembling the spokes of a wheel, shared housing and community buildings such as schools, shops, and administrative offices are located in hubs, and independently owned farmland radiates outward.
The Ponte della Libertà is the road bridge connecting the historical center of Venice (green), made up of 118 small islands within the larger Venetian lagoon, linked by canals or bridges to the Italian mainland to the west. Barrier islands and marshes can be seen in the eastern portion of the image, separated by the Faro di San Nicolò (St. Nicolas Lighthouse) and the Punta Sabbioni Leuchtturm flanking the western and eastern edges of the waterway opening to the Adriatic Sea. Floating along the meandering canals of the historic city center, glimpses of waterfront palazzos, small neighborhood churches, and grand cathedrals are revealed to visitors and locals alike.
The focal point of the image is the Forbidden City (the rectangular region in the upper left quadrant of the image). Urban or built-up areas appear in gold in the image, water bodies in black, and vegetated regions in blue. Some light yellow regions represent fallow/bare soil or particular building materials. The ring roads surrounding Beijing and the connecting linear road networks (dark gold/brown) illustrate movement within the city boundaries, as these roads link commercial centers and markets. They also illustrate how the urban network expands outward, enveloping the surrounding agricultural land, altering the land use of these regions.
EDITOR’S NOTE: This story was changed to correct an error in the original text that misstated the Imperial conversion of the 4-meter depth of the reservoir at Siem Reap. It should be 13 feet, not 2.5 feet.
Karen C. Seto is the Frederick C. Hixon Professor of Geography and Urbanization Science at the Yale School of Forestry and Environmental Studies and a member of the U.S. National Academy of Sciences.
Meredith Reba is research associate at the Yale School of Forestry and Environmental Studies.
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