The Art of the Chart
Somewhere in those symbols, lines, and colors is all the information you need to fly from here to there.
- By Stephan Wilkinson
- Air & Space magazine, November 1999
(Page 3 of 5)
Sectional charts are often taken for granted, yet they are printing and publishing accomplishments of immense complexity, acts of reproduction that approach an art form. Countless private pilots have papered their rec-room walls with sectionals, carefully pasted edge to edge to provide not only colorful wallpaper but a reminder of the enormous span of land that a set of wings can bridge. I don't know of any road maps that have been accorded the same honor. Unfortunately, you need Bill Gates' living room, or at least a wall 40 feet long and almost 20 high, to hang the 37 sectionals that cover just the 48 contiguous states. And there's one more for Hawaii and 16 for Alaska.
A typical sectional is almost five feet wide and more than a foot and a half high, printed on both sides. And like urban commuters who develop the ability to turn the pages of a newspaper in a packed subway car, pilots in cramped and often windy cockpits consider the proper folding and unfolding of a sectional a skill as important as leaning an engine's fuel mixture by ear. Even more demanding is the ability to pick up where you left off when your track suddenly migrates from one side of the sectional to the other. Indeed, each chart has instructions on how to handle that dilemma when you're plotting a course.
The compensation for the sectional's unwieldiness is the immensely satisfying proof of one's progress that comes when you move onto the Denver chart, say, and can fold up and put away the Wichita chart. Or, in the case of a slow airplane and a fast headwind, the equivalent is simply crossing a crease in the map and being able to rearrange the folds.
The base for each sectional--the primary map of the country's physical surface--is created from Department of the Interior Geological Survey 7.5 quadrangle maps, which are the delicately delineated maps that blanket the country in a scale so finely focused--each inch of paper is equivalent to a little over a third of a mile--that in rural areas, every house and barn is depicted. On a sectional, each quadrangle covers an area the size of a postage stamp, and it takes 2,000 of them to make up an entire sectional chart. (An inch on a sectional is just under eight miles.)
With the base established, each sectional is built from, typically, 53 layers of information, each layer a separate transparent sheet, all laid atop the map base. Each contains only the uniform graphics and color that are assigned to it. One layer has nothing but uncontrolled--airport symbols, little magenta circles with at most a runway or two shown. Another has control-tower airports, colored blue, with the runways depicted in scale. Another layer is nothing but man-made obstructions. Another: VOR (Very High Frequency Omnirange) compass roses. Another: yellow "urban tint" denoting built-up areas. Water. Highways. Drainage areas. Mountainous elevations. Radio-frequency boxes. Restricted areas. And so forth, amounting to, in the case of the particularly complex Los Angeles sectional, nearly 70 layers.
Continental U.S. sectionals are revised and reprinted every six months--twice the frequency of British and German air charts, which are generally considered to be in a class nearly as good as those of the U.S.--so the individual chart layers are constantly under revision. (Most Alaskan sectionals are renewed annually.) An updated master goes off to the printer every 28 days, since chart revisions are staggered to spread out the workload.
Changes can be wrought by everything from a private pilot calling AC&C (800 626-3677) with the news that the road west of Middletown shown as two lanes sure looked like four when he flew over it, to a mayor writing to announce that his town had just erected a new water tower and it would be swell if the chart honored it. Says Carl Nixon, chief of the Visual Chart Branch, "One of our best sources of new information is simply people flying around looking out the window. We get one or two tips a day, most of them phoned in."
Wander through AC&C's offices and you'll also see Rand McNally road atlases on many a desk. "We use the best available source of information," Nixon says, "whether it's a road atlas or a newspaper clipping." But this is only the first stage in a chart revision. AC&C never takes anything for granted, whether it's a phone call from a pilot, a letter from an electric company announcing completion of a power line, or even an official document from the Federal Aviation Administration. Everything is double-checked, sometimes by cartographers demanding photo verification.