Keywords: Adobe Photoshop, Blue Marble, Hal Shelton, Jeppesen Map Company, Library of Congress, MODIS Vegetation Continuous Fields, National Geographic Society, natural-color maps, National Land Cover Dataset, raster land cover data, satellite images, shaded relief, The Living Earth, Tibor Tóth, US Geological Survey.


INTRODUCTION

Natural-color maps are some of the most admired physical maps. The combination of land cover colors and shaded relief brings to the printed map a colorized portrait of the landscape that closely approximates what people see in the natural world around them. Green represents forest, beige represents desert, white represents ice and snow, and so forth. By basing map colors on the colors humans observe everyday in nature, the goal is to create physical maps that, despite their complex content, are easy to understand and more universally accessible to diverse audiences.

A discussion of American natural-color maps by necessity must start with the pioneering work of retired USGS (US Geological Survey) cartographer Hal Shelton for the Jeppesen Map Company during the 1950s and 60s. The first half of this paper offers a retrospective on Hal Shelton’s career and cartographic output, which, nearly fifty years later, still stands as some of the finest natural-color maps ever made (Figure 1). That he painted many natural-color maps with the apparent detail and realism of satellite images—years before the launching of the first satellites—is a visualization accomplishment worthy of our attention today.

Figure 1. A portion of Hal Shelton’s 1:5,000,000-scale New Europe map painted ca. 1968. The original measures 107 x 137 centimeters. Drainages and water bodies are photomechanical additions to the original art. Courtesy of Rand McNally & Company.


The second half of the paper fast-forwards to the present day. Drawing upon Shelton’s work as inspiration, we examine how to make natural-color maps digitally from raster land cover data derived from satellite imagery. We work with USGS National Land Cover Dataset and MODIS Vegetation Continuous Fields, produced by NASA and the University of Maryland. These two products detect, model, and classify land cover differently, which in turn affects the use of these data for cartographic presentation. Step-by-step instructions and illustrations show how to create polished natural-color maps from raw data. The design focus is on small-scale continental maps similar to those made by Shelton.


HAL SHELTON AND NATURAL-COLOR MAPS

Shelton’s development of natural-color mapping evolved over several decades and was not, in his words, “part of a grand design.” Nor was his entry into the cartographic profession.

The accidental cartographer

Hal Shelton was born in 1916 in New York State and moved with his family at an early age to southern California, where he grew up. Today he lives in the Rocky Mountain foothills above Denver, Colorado. His cartographic career began in 1938 after he graduated from Pomona College, California, with a degree in scientific illustration. Launching a career during the Great Depression with a background in art posed a challenge for Shelton. The only work that he could find was with a USGS field topography team conducting plane table surveys, starting out as a rod man. Although Shelton enjoyed mapping and working outdoors, he had other career aspirations. After one year with the USGS, he went back to college, received a Master of Arts degree in education, and took a teaching position with the San Diego school district. Shelton’s brief mapping career would have ended unnoticed at this point had it not been for the start of WWII (Shelton, 2004).

Because of his field mapping experience, during the WWII years Shelton found himself again employed by the USGS, mapping areas considered strategically important in the western United States. It was in the remote Jarbridge Mountains of northeastern Nevada that Shelton, now a full-fledged USGS topographic engineer, first began thinking about the presentation of terrain on maps, a process that would eventually lead him to natural colors (Shelton, 1985). Seeking place name information from the local residents, Shelton discovered that they could not read the contour map that he had just made. However, when he pointed across the valley to the rugged silhouette of the Jarbridge Mountains, the residents—there were seven in all—could readily identify Red Mountain, Old Scarface, and the other peaks. This experience convinced Shelton that the conventional symbology used on topographic maps was inadequate for depicting the landscape in a manner easily understandable by general audiences. The map symbology that he encountered was specialized and anachronistic even by 1940s standards. For example, the USGS manual at that time specified using a green tint for vegetation only for areas where you could hide a small detachment of troops or nine mules. Shelton—the artist, teacher, and by now a committed US government cartographer—was determined to find a better way.

Becoming a terrain artist

Shelton’s subsequent government assignments took him away from the field and to Washington, DC, Kansas, and finally to Colorado, where he spent the remainder of his career. Working indoors now, he began experimenting with shaded relief presentation, an effort that eventually paid off with his appointment as Chief Cartographic Engineer for the USGS Shaded Relief Map Program. Under Shelton’s direction the quantity and quality of shaded relief usage on USGS maps increased. His early shaded relief work included large-scale maps of Yosemite Valley, California, and Valdez, Alaska. These maps emphasized topographic form and relative elevation by combining brown shaded relief with a green lowland tint, overlaid with lightly printed contours. His relief presentation style during this time was strictly conventional.

Shelton’s first attempt at natural-color mapping occurred while on temporary duty with the US Air Force. His primary assignment was designing aeronautical charts for use in airplane cockpits in low light conditions. Of greater relevance to our story was another assignment redesigning an aeronautical chart of a remote corner of the Sahara (for use under full lighting). The replaced chart used conventional symbology—a dense network of blue lines portrayed intermittent wadis and a green tint filled lowland areas all but devoid of vegetation. According to Shelton, using this chart “would tempt a pilot to land and go trout fishing.” Referring to the realism of aerial photography, Shelton redesigned the chart to appear appropriately arid mimicking the view seen by a pilot flying over the area. Because lines rarely occur in nature (Shelton firmly believes in avoiding the use of lines on maps wherever possible), the new chart depicted wadis as light streaks across the brown desert floor. Shelton also depicted volcanic rocks with rough-textured dark tones. The original chart based on conventional symbology lacked a way to depict these areas, so its author resorted to a label stating “area of dark rocks.” According to Shelton, such text labels are evidence of a map’s failure to communicate. Nor is he keen about legends, which he views as unnecessary on a properly designed map. He defines a map as

“A graphic instrument of communication that transfers information from the awareness of a person with information to the awareness of a person without that information.”

“It smells different on top of a mountain than it smells down in the valley, it sounds different at the top. As you climb… you’re getting a tremendous amount of information.”

“…to smell the mountain and hear the wind.”

This mix of mostly vegetation zones and physiographic formations may seem eclectic at first glance. All of the categories, however, are well suited for distinctive depiction on a map. The goal after all was making readable and informative maps as opposed to classifying world land cover in a scientifically consistent manner. Thinking that too many colors might overwhelm the reader, Shelton favored using fewer categories but the other team members convinced him otherwise. Judging by the readability of the finished plates, his concerns did not materialize, no doubt because of the artistic skill he applied to the task. In a classification dominated by nature, the inclusion of farmland is noteworthy because it acknowledges the impact of humans on the land—a fact plainly obvious to anyone flying over the checkerboard fields of the US Midwest. With crosshatched brush strokes Shelton represented these field patterns on his maps. Built up areas are the one major land cover category conspicuously absent from Shelton’s painted bases. Admittedly, however, urban sprawl was not nearly as widespread then as it is today. To depict urban areas on the Jeppesen maps, bright yellow area tones were applied photo mechanically in a second step for final printing.

Figure 2. Shelton’s standardized palette of natural colors captured the character of disparate geographic regions worldwide. Courtesy of Rand McNally & Company.

Shelton/Jeppesen maps covered all areas of the globe. Uses included wall maps and textbook maps for schools and colleges, commercial promotion, and passenger maps for many airlines (Library of Congress, 1985). Because of their detail and realism, NASA used these maps to locate and index photos of Earth taken on early space missions (Figure 3).

Figure 3. (left) Excerpt of a natural-color map painted by Hal Shelton ca. 1968. (right) NASA MODIS satellite image taken in 2003. Map on left courtesy of Rand McNally & Company.

In 1961, Elrey Jeppesen sold his firm to the Times Mirror Publishing Company of Los Angeles but remained as president. Hal Shelton also continued working for the new owners until the late 1960s. In 1985, the HM Gousha Company, a subsidiary of the Times Mirror Publishing Company, donated 29 original plates painted by Hal Shelton to the US Library of Congress. The Shelton Collection, as it is now called, has grown to some 33 plates and miscellaneous other materials. Rand McNally & Company in 1996 acquired the assets of HM Gousha, which no longer exists, thereby inheriting copyright ownership of Shelton’s plates housed at Library of Congress (see Appendix A). The Shelton Collection can be viewed by appointment in the Map Reading Room.

Cartographic contemporaries

Shelton’s colleagues in the cartographic profession influenced his thinking about natural-color maps, particularly those from the Alpine countries of Europe. The famous Walensee Map painted by Eduard Imhof in 1938, which masterfully combines land cover colors and shaded relief, directly influenced Shelton. Shelton and Imhof met in 1958 at the 2nd International Cartographic Conference in Chicago, the so-called “Rand McNally” conference. At this conference Imhof praised Shelton’s natural-color maps saying, “there is nothing more that I can contribute.” However, the two men did not see completely eye to eye. Afterwards Imhof visited Shelton at his studio in Golden, Colorado, for about a week. According to Shelton, they politely agreed to disagree on the use of color on physical maps. Imhof favored using color exclusively for modeling topographic forms and depicting altitude, arguing that combining land cover colors with shaded relief only weakens the presentation of topography. Discussing Shelton’s work in his 1982 text, Cartographic Relief Presentation, Imhof states

“At the small scale, however, the relief forms and the ground cover mosaic are so finely detailed and often have so little relation to one another that in certain areas great complexity and distortions of the relief are unavoidable. As a result of the flatness and spaciousness of the “models,” distinct aerial perspective hypsometric tints can scarcely be achieved by such combinations.”

Imhof’s point is valid—if one’s sole aim is portraying topography on a physical map. Shelton’s approach to physical mapping, however, is more holistic. Shelton regarded the physical world not as a cartographic abstraction, such as elevation above sea level, but as the colors and forms processed by his mind from reflected light observed outdoors. What was on the terrain surface mattered as much as the terrain surface itself. If a landscape looked arid and sun bleached, so too should its depiction on a map.

Shelton’s closest cartographic soul mate from Europe was, perhaps, Heinrich Berann of Austria. Like Shelton, Berann came from an art and illustration background and painted panoramic maps lavishly adorned with colors depicting land cover and vegetation (Patterson, 2000). Shelton departed from Berann’s technique in using natural colors on plan maps viewed from directly above. Although Shelton never met Berann, he admired his work. He once had a German-speaking neighbor on vacation call on Berann to obtain his color formulas. A page and a half of detailed instructions on paint mixing resulted from the visit. However, Shelton found Berann’s palette to be based more on artistic considerations than observed nature, so he devised his own. One of Berann’s colors that did find its way into Shelton’s palette, however, was yellow-green for depicting humid grasslands, pastures, and meadows. Bright and decidedly unnatural, this green occasionally detracts from Shelton’s otherwise balanced colors, at least according to the authors’ tastes. The primitive color printing of that time only exacerbated this problem. To be fair to Shelton, nearly all terrain artists from that era relied on this particular shade of green; such was the dominant influence of Heinrich Berann.

On this side of the Atlantic, Richard Edes Harrison was a contemporary of Shelton’s in the arena of cartographic relief presentation. He was renowned for creating artistic “over-the-horizon maps” for Fortune magazine, and shaded relief plates containing fine physiographical detail. Both men were similar in that they came to cartography from illustration backgrounds, and they were both innovators and cartographic populists. Harrison colored his maps in a conventional manner, which offered no guidance to Shelton’s development of natural colors. However, Harrison’s monochromatic portrayal of textured lava flows, sand dunes, and other physiography influenced Shelton’s mapping style, which gained in detail over the years (Shelton, 2004).

Why natural colors?

In terms of willingness to experiment with color, Shelton fell somewhere between the conventional colors preferred by Imhof and Harrison, and the uninhibited end of the color spectrum preferred by Berann. A half-century ago the key players in the field of relief presentation strongly espoused differing styles. Shelton was in the middle of this fray. The central point of debate then—which continues today but with considerably less fervor—was over appropriateness of hypsometric tints (colors assigned to elevation zones). Shelton regarded hypsometric colors as “arbitrary” and as bearing little relation to the actual color of the land, such as a green lowland tint filling parched desert basins, and red applied to uplands where forests grow. Classic hypsometric tints inverted the sequence of elevation-influenced natural colors observed by Shelton in the landscapes of the US West (Figure 4).

Figure 4. (left) A shaded relief map of southwestern United States combined with natural colors. (right) The same map with blended hypsometric tints. Although hypsometric tints are attractive and show topography clearly, they can mislead readers about the character of the land. Forests cover the Yellowstone region and Yuma, Arizona, is an extreme desert environment.

Based on the large quantities of maps that display hypsometric tints, an anthropologist a thousand years from now might conclude that our society was elevation-centric. However, the current popularity of hypsometric tints has more to do with production ease and pretty colors than it does with our interest in elevation. Making competent hypsometric tints requires mere minutes to accomplish with a digital elevation model and freeware software. Even the photomechanical techniques of yesteryear were relatively straightforward, albeit much slower. With hypsometric tints, the end result is often a map with pleasing colors that blend softly into one another in an orderly fashion, a design trait that people find attractive, even if they don’t necessarily know or care about elevations. To the average reader the elevation zone between 750 and 2,000 meters in California, for example, which can assume any color in the rainbow on a hypsometric tint map, is artificial, abstract, and, to use Shelton’s favorite term, arbitrary.

By contrast, natural colors on a map are less susceptible to misinterpretation. For example, color-sighted humans tend to associate green with the color of vegetation, brown with aridity, and white as the color of snow (at least people living in the mid and high latitudes). The Nevada residents interviewed by Shelton 60 years ago had named Red Mountain because of its distinctive cast. Recent psychological research suggests that bright colors attract our attention—not really a surprise—and that our memory retention improves on images comprised of natural colors compared to false colors or black and white (Gegenfurtner et al., 2002). Considering the potential for natural-color maps to easily, and perhaps lastingly, communicate geographic information to the user, why then are they so rare? The short answer: they are tremendously difficult to make.

The making of natural-color maps manually requires that a cartographer possess singular artistic talent, broad knowledge of physical geography, and patience—combined traits that are in short supply, particularly where costs are determining factors. Natural-color maps are handcrafted and expensive products. One occasionally sees gaudy, unrefined attempts at natural-color mapping published in tourist brochures, proof that not everyone qualifies for the job title: artist/cartographer. Working with colored pencils, airbrush, watercolors, and acrylics, one of the authors of this article tried over the course of many years to create such maps, but met with only limited success. Creating a tabloid-sized map of moderate complexity required two to three weeks of work with the constant worry that the airbrush could splatter without warning and ruin everything. Shelton was considerably faster in applying pigments to maps. Providing that he had a clear and accurate base to work from, a typical large natural-color map would take about 40 hours to paint (Shelton, 2004).

We must also bear in mind that natural-color maps are not appropriate for all types of general or even physical mapping. The merging of shaded relief and land cover, regardless of how delicately done, creates a level visual weight and background complexity that may detract from other classes of information depicted on the map. Nothing good comes from printing area colors, such as polygons showing property ownership, on top of natural-colors, or on hypsometric tints for that matter.

Natural-color bases are suited for use with uncluttered general reference maps and thematic maps where the surface environment and interconnectedness matters most. They are most appropriately used at small and medium-scales where the natural colors combine with shaded relief to create textures that appear organic and plausibly realistic. Larger map scales, however, require supplementary bump map textures (a type of 3D embossment) to achieve similar results (Patterson, 2002). Although some cartographers may be loath to admit this as a valid use, natural-color maps make outstanding wall decorations. Even today the airline route maps published by Jeppesen are still one of the best uses ever found for natural-color maps.

Moving forward

Today, the foremost practitioner of natural-color mapping is Hungarian-born Tibor Tóth, formerly an employee of National Geographic, and now working freelance. Readers of the National Geographic Atlas of the World would quickly recognize Tóth’s work. Showcased prominently, his painted plates of the physical world and continents are associated by many with the distinctive look and feel of National Geographic maps. Toth, a talented artist and cartographer in his own right, consulted with Hal Shelton at his Colorado studio in early 1971. Tóth then developed a natural-color mapping style modified and distinct from Shelton’s, which he first applied to a map of Africa later that same year (Tóth, 1986). Instead of showing existing land cover as Shelton did, Tóth’s maps use color to show potential vegetation based on biogeographer AW Küchler’s data. Potential vegetation shows readers a more abstract interpretation of the landscape without human influences. Imagine if you will, untrammeled North America before the first humans arrived from Asia.

Tóth—before switching to digital production—painted and airbrushed his maps from a standardized palette formulated by carefully mixing paints drop by drop (Tóth, 1973) (Figure 5). The National Geographic tradition in natural-color mapping continues today thanks to Tóth’s successor, John Bonner (Tóth also continues to work freelance for NG). Bonner’s magnum opus was a 3.35-meter-wide globe airbrushed and painted with natural colors that was on display at Explorers Hall in Washington, DC, for more than a decade, up until 2000.

In 1985 the Library of Congress, Geography and Map Division interviewed Hal Shelton on videotape. During the 51-minute interview Shelton stated his hope that new people and techniques would continue the process of natural-color mapping into the future. He concluded the interview with the advice

“…that we can be flexible enough to recognize change, and be wise enough to understand those things that don’t change so much, which is the need to have human beings to communicate.”

Turning now to the digital part of this paper, we attempt to follow his advice.