GIS is both intuitive and cognitive. It combines powerful visualization and mapping with strong analytic and modeling tools. Remotely sensed earth observation—generally referred to in GIS circles simply as imagery—is the definitive visual reference at the heart of GIS. It provides the key, the geographic Rosetta stone, that unlocks the mysteries of how the planet operates and brings them to life. When we see photos of Earth taken from above, we understand immediately what GIS is all about.
The story of imagery as an Earth observation tool begins with photography, and in the early part of the 20th century, photography underwent extraordinary changes and social adoption. Photos not only offered humanity a new, accessible kind of visual representation—they also offered a change in perspective. The use of color photography grew. Motion pictures and television evolved into what we know today. And humans took to the sky flying in airplanes, which, for the first time, enabled us to take pictures of the earth from above. It was a time of transformation in mapping and observation, providing an entirely new way of seeing the world.
During World War II, major advances in the use of imagery for intelligence were developed. The Allied Forces began to use offset photographs of the same area of interest, combining them to generate stereo photo pairs for enhancing their intelligence gathering activities. In one of many intelligence exercises called Operation Crossbow, pilots flying in planes—modified so heavily for photo gathering that there was no room for weapons—captured thousands of photographs over enemy-held territory. These resulting collections required interpretation and analysis of hundreds of thousands of stereo-pairs by intelligence analysts.
These 3D aerial photographs enabled analysts to identify precise locations of highly camouflaged rocket technology developed by Germany. This was key in compromising the rocket systems that were targeting Great Britain, thus saving thousands of lives and contributing to ending World War II. The BBC did a comprehensive documentary on this subject (Operation Crossbow: How 3D Glasses Helped Defeat Hitler).
In the early 1960s, the majority of people would probably have said it was impossible for a human being to walk on the moon. But in July 1969, televised images transmitted to Earth from the moon showed Neil Armstrong and Buzz Aldrin bounding across the lunar surface, proving that moon walking was more than conceptually possible—it was happening right before our eyes. Seeing was believing.
When Armstrong, Aldrin, and the ensuing lunar astronauts pointed their cameras back at Earth, an unexpected benefit became apparent: humanity now had a completely new perspective about our home planet—heralding the adoption and use of Earth imagery (see “Earth from Space” below).
In 1972, the same space technology that was developed to put humans on the moon led to the launch of the first Landsat satellite. The Landsat mission gave us extraordinary new kinds of views of our own planet. This was a breakthrough system and the first civilian-oriented, widely available satellite imagery that not only showed us what was visible on Earth—it also provided a view of invisible information, unlocking access to electromagnetic reflections of our world. We could see Earth in a whole new way.
This persistent earth observation program continues to this day along with hundreds of other satellites and remote sensing missions as well. Nation states and, more recently, private companies have also launched numerous missions to capture earth imagery, allowing us to continuously observe and monitor our planet.
Little more than a decade ago, seemingly the whole world snapped awake to the power of imagery of the earth from above. We began by exploring a continuous, multiscale image map of the world provided online by Google, Microsoft, and other companies. A combination of satellite and aerial photography, these pictures of Earth helped us experience the power of imagery, and people everywhere began to understand some of what GIS practitioners already knew. We immediately zoomed in on our neighborhoods and saw locational contexts for where we reside in the world. This emerging capability allowed us to see our local communities and neighborhoods through a marvelous new microscope. Eventually, naturally, we focused beyond that first local exploration to see anywhere in the world. What resulted was a whole new way to experience and think about our planet.
These simple pictures captured people’s imagination, providing whole new perspectives, and inspired new possibilities. Today, virtually anyone with Internet access can zero in on their own neighborhood to see their day-to-day world in entirely new ways. In addition, people everywhere truly appreciate the power of combining all kinds of map layers with imagery for a richer, more significant understanding.
Almost overnight, everyone with access to a computer became a GIS user.
Seeing is believing. Observing the world in colorful imagery is informative and immediate, delivering stark visual evidence and new insights. Imagery goes far beyond what our own eyes are capable of showing us—it also enables us to see our world in its present state. And it provides a means to look into the past as well as forecast the future, to perceive and understand Earth, its processes, and the effects and timelines of human activity. Amazingly, imagery even allows us to glimpse the invisible, to see visual representations of reflected energy across the entire electromagnetic spectrum, and to thus make more fully informed decisions about the critical issues facing Earth and all its life-forms.
Global imagery is collected continuously, enabling us to witness our world in action. By combining images from across the span of time, we can begin to visualize, animate, analyze, and understand Earth’s cycles, where we came from, and where we are going.
Imagery enables us to see beyond what our human eyes perceive, providing new scientific perspectives about Earth. Satellites have sensors that measure nonvisible information, such as infrared energy, across the electromagnetic energy spectrum that enables us to generate and analyze a multitude of new terrestrial views of our world.
Advances in imaging and weather observations over the last decade have resulted in a dramatic increase in the accuracy and precision of meteorologic forecasts. GIS integration of climate data for operations management has expanded to benefit farmers, emergency response teams, school districts, utilities, and many others. The sensors range from global weather satellites to ground-based local instruments that allow experts to monitor and forecast meteorological events like never before. The sensor network has become hyperlocal, allowing continuous forecasting of weather events in our communities. We can now access an accurate forecast for our neighborhood for the upcoming hour.
Imagery lets us to peer into the past as well as combine historic views with current imagery. Imagery comes in a simple format, allowing it to be easily overlaid with other maps and images into a kind of layered “virtual sandwich.”
A special relationship has always existed between GIS and remote sensing, and it goes back to the very beginning of our modern information technology. In the 1960s and 1970s, computer systems for GIS were big, expensive, and very slow mainframes using punched cards, but nearly all the foundation data layers in these early systems came either directly or indirectly from imagery. Right from the start, GIS and remote sensing were complementary, like two sides of the same coin. They coevolved together.
In 1972, a revolution happened with the launch of Landsat—the first commercial Earth observation imaging satellite. It continuously orbited the earth and captured a new image of the same spot about every 16 days. Because it was so high up, it gave us an entirely different picture of our planet and its patterns. It provided not only a new view; it gave us a new vision of the possibility of what GIS could become. And it started a revolution in commercial Earth observation that continues today and is exploding now with hundreds—and soon thousands—of smaller satellites, microsatellites, video cameras from space, high-altitude drones, and more.
So where are GIS and remote sensing—these two close allies for more than 50 years—going next?
For one thing, there’s a big emphasis now on simplicity and speed. It’s clear that the future belongs to the simple and quick. We’re seeing that modern technology is harnessing this amazing array of globally distributed sensors into what is popularly referred to as the Internet of Things, a vast collection of dynamic, live information streams that are feeding into and becoming the heart of Web GIS. Plus, this network operates in real time, giving us access to what we might call the “Internet of All My Things”—and all on our own devices through a new geoinformation model.
Although the technology powering this concept is advanced, we comprehend it in practice because we understand pictures. Einstein famously said, “If I can’t see it, I can’t understand it.” We all know something when we can see it.
And now, all these rapidly changing developments combining imagery and spatial analyses are opening up new chapters in the history of GIS, as society is awakening to the power of geography and the intuitive understanding that imagery helps us “see” in all its forms.
We like to say that the map of the future is an intelligent image.
By now, it’s apparent that imagery enables whole new perspectives and insights into your world and the issues you want to address. Imagery also has numerous advantages and capabilities.
Image collection is rapid and increasing. And access to imagery is increasingly becoming more responsive. Many satellites and sensors are already deployed with more coming all the time, collecting new data, adding to a continuous collection effort—a time series of observations about our planet. These image collections are enabling us to map, measure, and monitor virtually everything on or near the earth’s surface. All of us can quite rapidly gather much of the data that we need for our work. Imagery has become our primary method for exploration when we “travel” to other planets and beyond. We send probes into space and receive returns primarily in the form of imagery that provides a continuous time series of information observations. And it enables us to derive new information in many interesting ways.
The use of aerial imagery is still relatively young. Although imagery began to be used only in the 20th century, it is easy to compare observations for existing points in time that reside in our imagery collections. In addition, we can overlay imagery with historical maps, enabling us to compare the past with the present.
Imagery is leading to an explosion of discovery. Many imagery initiatives are growing, expanding, and adding to image databases for our areas of interest. ArcGIS includes a complete image processing system, enabling the management of increasingly large, dynamically growing Earth observations. This points to the immediacy of imagery and its capacity for easy integration, enabling all kinds of new applications and opportunities for use—things like before-and-after views for disaster response, rapid exploration of newly collected imagery, image interpretation and classification, and the ability to derive intelligence. Over time, many of these techniques will grow in interesting new ways, enabling deeper learning about our communities, the problems and issues we face, and how we can use GIS to address them.
Imagery and its general raster format enable rich analysis using ArcGIS. And, in turn, these analyses enable more meaningful insights and perspectives about the problems you want to address.
Imagery in all its variations uses one of the key common data formats in GIS: rasters. Rasters are one of the most versatile GIS data formats. Virtually any data layer can be conveyed as a raster. Using rasters, you can combine all kinds of data with your imagery, enabling integration and analytics.
Rasters, like any digital photo, provide a data model that covers a mapped area with a series of pixels or cells of equal size that are arranged into a series of rows and columns. Rasters can be used to represent pictures as collections of pixels, surfaces such as elevation or proximity to selected features, all kinds of features themselves (in other words, points, lines, and areas), and time series information with many states for each time period.
Land cover around the western Mediterranean, from a global raster dataset from MDA Information Systems of the predominant land characteristics at 30-meter resolution.
A proximity map showing distance from each cell or pixel to a reliable water source in a portion of West Africa. Water access is vital for humans as well as wildlife habitat. Streams are overlaid on the distance grid. Cells in the grid that are closest to water are darker blue. Colors change as the distance from water increases.
Mont Blanc or Monte Bianco in the Alps between France and Italy is included in this app (linked above), which features a 3D tour of interesting sites from around the world.
Oblique imagery provides a special perspective view of real-world features, presenting natural detail in 3D and enabling interpretation and reconnaissance.
Global elevation displayed as shaded relief. This is part of a global elevation layer compiled from the best available sources worldwide.
A snapshot of a time-enabled image map of monthly snowpack observations from the NASA Global Land Data Assimilation System (GLDAS). This map contains cumulative snowpack depths for each month from 2000 through 2015.
While imagery provides whole new perspectives, profoundly shaping our understanding, it’s also clear that imagery provides exquisite views of our world—truly stunning and beautiful works of art. They astonish and amaze us, tapping into our emotions and the wonder of our world and new worlds we seek to discover and explore. It’s no accident that the US Geological Survey maintains a collection of Earth as Art.
In the run-up to the Apollo moon landings, Apollo 8 was the first mission to put humans into lunar orbit. And on Christmas Eve 1968, coming around from the far side of the moon during their fourth orbit, Apollo 8 commander Frank Borman exclaimed, “Oh my God, look at that picture over there! Here’s the earth coming up! Wow, that is pretty!” Fellow astronaut Bill Anders grabbed his Hasselblad camera and shot this now-famous image of Earth rising above the moon.
In his book Earthrise: How Man First Saw the Earth, historian Robert Poole suggests that this single image marked the beginning of the environmental movement, saying that “it is possible to see that Earthrise marked the tipping point, the moment when the sense of the space age flipped from what it meant for space to what it means for Earth.” The power of imagery can be neatly summed up in the story of this single photograph. Images can help us better understand our planet, drive change, create connections—and in some cases even start a movement.
Since the first moon shots, astronaut-photographers from the world’s space agencies have also been turning their lenses away from Earth. GIS people, being the science fanatics they often are, have of course found ways to map planetary bodies other than our home planet. In 2015, NASA announced to the world that multispectral imagery taken from Mars-orbiting sensors had definitively ascertained the one-time presence of moving water on Mars—a milestone not lost on the GIS and image analysis community.
Imagery appears throughout the ArcGIS platform. Here are two starting points.
Accessed billions of times monthly, the ArcGIS Imagery and Imagery with Labels basemaps are the most popular background maps that people use for their GIS projects. Imagery serves as a canvas to provide context and validation for your GIS data.
Landscape analysis underpins much of our land-use planning, how we manage natural resources and their relationship with the environment. The landscape layers in this group are configurable and provide access to hundreds of measures about aspects of the people, natural systems, and plants and animals that define the landscape of the United State and the rest of the world.
In this lesson, you’ll explore Landsat imagery and some of its uses with the Esri Landsat app. You’ll first go to the Sundarbans mangrove forest in Bangladesh, where you’ll see the forest in color infrared and track vegetation health and land cover. Then, you’ll find water in the Taklamakan Desert and discover submerged islands in the Maldives. After using 40 years of archived Landsat imagery to track development of the Suez Canal over time, you’ll be ready to explore the world on your own.
Satellite imagery is an increasingly powerful tool for mapping and visualizing the world. No other method of imagery acquisition encompasses as much area in as little time. The longest-running satellite imagery program is Landsat, a joint initiative between two US government agencies. Its high-quality data appears in many wavelengths across the electromagnetic spectrum, emphasizing features otherwise invisible to the human eye and allowing a wide array of practical applications.