Chapter 5

Getting the Message of Maps

In This Chapter

bulletKnowing what a map is showing

bulletMeasuring distance and size

bulletTaking a look at graphics

bulletUsing symbols to depict reality

bulletFinding ways to gather information

bulletHarnessing new technologies for an old medium

W hen I was an adolescent, one of my prized possessions was a big world atlas. I’d sit in my room for hours at a time just pouring over pages I had randomly turned to. While it was all very mesmerizing and fascinating, one day, a disturbing thought occurred to me: Most teen-aged boys don’t do this. What’s wrong with me?

Over the years, and much to my relief, I met numerous geography teachers and students who, however meekly, admitted to similar habits. Indeed, such behavior turns out to be perfectly normal for people who, whether or not they know it, have a yen for geography. No doubt, that is because the map is the most basic geographical tool.

Complementing the previous chapters on Earth’s grid and the properties of projections, this chapter focuses on ways in which maps communicate information and how some of that information is obtained. Basically, this chapter is about map reading and map information for the novice. Therefore, if you are, in fact, one of those people who can stare at maps for hours, then you can probably skip this chapter. But if maps confuse you or seem overwhelming, or if you have never been taught the fundamentals of maps and map reading, then this chapter is for you. While you probably won’t master all there is to know, you can familiarize yourself with enough fundamentals so that you get the message of maps.

Checking Out the Basic Map Components

The basic function of maps is to show how particular phenomena are distributed over all or part of the world. In this chapter, for example, you will see maps of Canadian cities, languages in South America, and global migration to the United States. Cartographers (mapmakers) communicate these and other kinds of information in part by incorporating into their maps a standard set of elements whose purpose is to help the map-reader get the message. They include the following:

Tip

bulletTitle: The title conveys the subject of the map and is the first thing a map-reader should look for. Ideally, its wording is simple and accurate. If the title confuses you, then that is probably more of a comment on the cartographer’s communication skills than your intelligence quotient.

bulletLegend: Maps commonly convey information with the aid of symbols whose meanings may be uncertain. Thus, the cartographer always provides a legend (or key) that contains and defines the symbols found on the map.

bulletScale: Scale (described more fully in the following section) provides information about the actual size of the area shown on the map. Typically, this is achieved with a small ruler-like entry on a map that equates distance in miles and/or kilometers with measurement in inches and/or centimeters.

bulletOrientation: Orientation is the alignment of the map with respect to cardinal directions. Which way are north, south, east and west? The standard rule of thumb is that north is towards the top of the map, but not every layperson knows the rule and not every map follows it. Accordingly, many maps include a direction indicator, minimally a north-pointing arrow. While one is included in Figure 5-1 for the sake of example, they are not common on maps of large areas because cardinal directions may vary due to distortion (see Chapter 4). Also, if latitude and longitude lines are included, then the cardinal directions are somewhat redundant.

bulletGrid lines: Many maps contain a couple of labeled grid lines of latitude and longitude in order to convey the global context of the mapped area. If the cartographer has reason to believe that the map reader is intimately familiar with the mapped area, or if previous maps have indicated the global context of the mapped area, then grid lines may be omitted.

bulletSource: Out of courtesy and honesty, cartographers commonly provide the source of the information conveyed on the map. This is especially true for maps that portray numerical data. On the other hand, some subjects are generally considered “common knowledge” and do not require source citation. Examples include maps of countries, physical features, and climates.

bulletBorder and neat line: Maps are commonly contained within a border that assumes a conventional geometric shape, usually a rectangle. The purpose is largely aesthetic, though in books and articles borders serve the practical function of clearly differentiating map and text. Typically, borders are bold lines. Often they frame a thinner neat line whose purpose is purely aesthetic.

Taking It to Scale

Remember

Scale is the relationship between a distance as measured on a map and the corresponding actual distance on Earth’s surface. Calculating distance between locations and comparing the size of areas are two of the more important functions of maps.

Going the distance

The scale of a map may be stated in three rather different ways, described in the following sections. Figure 5-1 shows you what the three ways look like. Some maps include just one of them. Others include two, and still others all three. Perhaps the most important thing to remember is that every map has a single scale, but a cartographer has three ways to tell you what it is. If, therefore, a single map contains two or three of the scale-types, then each is saying the same thing, albeit in a different way.

Bar graph

A bar graph looks like a miniature ruler. But, whereas the ruler you use may show inches and millimeters, the one on the map shows miles and kilometers, (as shown in Figure 5-1). The principal virtue of the bar graph is that it provides a clear visual reference to the size of the area portrayed on the map. For actual measurement, however, it may be a bit unwieldy because you can’t pick it up like you can a real ruler.

Verbal scale

A verbal scale (also called statement of scale) communicates the relationship between map distance and real-world distance in a sentence or sentence-like format. In Figure 5-1, “One inch equals one mile” is the example. If you have a foot ruler handy, apply it to the bar graph and confirm that a distance of one mile as indicated on the bar graph is, in fact, an inch in length. Again, a given map has a given scale, and therefore the different ways of expressing that scale must agree, which is precisely what your ruler should demonstrate.

As far as most people are concerned, the verbal scale is particularly convenient for measuring distances on a map, provided a ruler is available. In the case of “one inch equals one mile,” one need only measure the number of inches between two points to arrive at the number of miles that separate them on Earth. If, on the other hand, the verbal scale on another map reads “one inch equals 20 miles,” then the number of inches between the two points on the map needs to be multiplied by 20 to render the actual distance.

Remember

Maps come in different scales. Thus, the scale you use to calculate distance on one map may not be the same for the next map. Always check the scale before you calculate distance.

Whence comes the mile?

A mile is a unit of linear measurement that equals 5,280 feet. While most of the world has adopted metric units (kilometers), Americans continue to express distance in miles, which, therefore, commonly appear as units of measurement on maps made in the U.S. But exactly what is a mile? And why does it consist of 5,280 feet instead of a more convenient figure, like 5,000?

“Mile” comes from the Latin milia, meaning thousand. In Roman times, a unit of linear measure called the milia passum, or thousand paces, was common. Somehow, somebody’s thousand strides became a standard Roman mile, equal to about 1,650 yards. This measurement became widely used in Britain following the Roman’s invasion. After the Empire’s demise, however, the milia passum fell into disuse, although “mile” endured in the British vocabulary as a word applicable to a substantial distance.

The mile’s present length has its origins in medieval English agriculture. Back then, a team of oxen was used to pull a heavy wooden plow. The farmer walked behind, making liberal use of an ox goad — a big stick — to influence the animals’ behavior. The stick was known as a rod, and at some point its length was standardized to 16.5 feet. The length of a parcel of farmland was “a furrow long,” or furlong. That was the distance the oxen could pull the plow before the farmer had to stop and rest them. Naturally, that length varied. In time, however, the furlong was standardized to a distance of 40 rods (660 feet or 220 yards). Sometime later, a distance of 8 furlongs (5,280 feet or 1,760 yards) became the standard mile, and remains so to this day.

Representative fraction (RF)

TechnicalStuff

The area shown on a map is a fraction of its actual size. Appropriately, therefore, scale may be indicated as a representative fraction (RF), which states the ratio between a unit of distance on the map and the same distance measured in the same units on the ground. As far as most people are concerned, this is the most confusing scale-type and the most difficult to explain. OK, here goes.

Check out Figure 5-1 again. The RF shown is 1:63,360. That means the map is 1/63,360th the size of the area it shows. Stated differently, a distance of one inch on the map equals 63,360 inches on the Earth’s surface.

Once more, a given map has a given scale, but you can express it in different ways. In the example, therefore, “One inch equals one mile” and “1:63,360” must mean the same thing. And, indeed, they do. Proof is obtained by calculating the number of inches in a mile. To do that, multiply the number of inches per foot times the number of feet per mile (12 × 5,280). The answer is 63,360, so the statement of scale and the RF are, in fact, the same.

Comparing Earth at different scales

Remember

Maps come in different scales; and because they do, the amount of area and degree of detail shown on one map may be very different from another. This is demonstrated in Figure 5-2, which shows three maps that have identical dimensions and progressively “zoom in” on Chicago. Specifically:

bulletIn Figure 5-2a, 1 inch represents 630 miles. As a result, this map shows a comparatively large area that includes most of the Great Lakes, Upper Midwest, a handful of major cities, and a portion of Canada.

bulletIn Figure 5-2b, 1 inch represents 190 miles. What is shown now is a much smaller area that includes parts of Lake Michigan and Midwest states, a few medium-size towns, and a few major regional highways.

bulletIn Figure 5-2c, 1 inch represents 64 miles. Now we have “zoomed in” to the extent that the map shows Greater Chicago, southern-most Lake Michigan, more municipalities, local highways, and several streets.

Notice that as the area shown on these maps decreases, the amount of detail increases. And if you think about it, that makes a great deal of sense. When 1 inch represents 630 miles — a large area — only very large surface features (such as the Great Lakes) can be shown. But when 1 inch represents 64 miles — a much smaller area — then comparatively small surface features (such as roads) can be effectively shown.

TechnicalStuff

In the lingo of cartography, small scale maps show large areas in little detail, while large scale maps show small areas in big detail. Figure 5-2a has a comparatively small scale. In contrast, Figure 5-2b has a somewhat larger scale, while Figure 5-2c has the largest scale among the three maps. And indeed, as the scales of these maps get larger, the degree of detail increases.

Showing the Ups and Downs: Topography

All points on Earth have an elevation with respect to sea level. Altogether, they constitute “the lay of the land.” (Keep in mind that elevation also pertains to points on the ocean’s bottom.) Topography is the art and science of depicting heights and depths on a map. Like scale, topographic information is a basic feature of many maps and is commonly represented in three ways as indicated in Figure 5-3. The following sections discuss the three ways of showing topographic information.

Spot heights

A spot height is a symbol (typically a tiny dot, plus sign, or triangle) accompanied by a number that indicates the elevation of a given point in feet or meters (see Figure 5-3a). Sometimes a cartographer wishes to emphasize something other than topography on a map, yet provide elevation information for a few selected points in order to convey the lay of the land. Spot heights serve this purpose.

Distortion for a purpose

A cartogram is a map in which different areas are distorted in proportion to numerical data. Following are two maps of Australia. The one on the left shows the true shape of the continent. The one on the right is a cartogram in which the sizes of Australia’s states and territories are distorted in proportion to their populations. As a result, the cartogram looks much different than the “real thing.” New South Wales, which is home to Sydney (the nation’s largest city), contains about 10 percent of the country’s territory, but about 34 percent of its population. On the cartogram, therefore, New South Wales appears bloated. In contrast, Northern Territories accounts for 17 percent of the country’s territory but only 0.01 percent of its population. On the cartogram, therefore, Northern Territories is quite small. These extremes visually highlight Australia’s uneven population geography. Usually, cartographers seek to minimize map distortion. In the case of cartograms, however, distortion is the purpose of the exercise.

Contour lines

Contour lines connect points of equal elevation. In so doing, they convey the shape (hence, “contour”) of the land they depict. Near the top of Figure 5-3b is a thin line labeled “50,” which connects points that are 50 feet above sea level. Farther inland is a line labeled 100, which connects points that are 100 feet above sea level. Thus, a walk from the water’s edge to a point on the second line involves a 100-foot gain in elevation.

Shading

Colors and gray tones may also be used to indicate elevation above sea level. On color maps, deep green is usually used to depict low-lying coastal land. Light green and yellow are used for progressively higher lands, followed by light brown and dark brown. The peaks of really high mountains are often shown in white.

Tip

When gray tones are used in cartography, the general rule of thumb is “the darker the gray tone, the greater the value of whatever is being mapped.” Accordingly, and as seen in Figure 5-3c, the lightest shade indicates the lowest-lying land, while deeper shades signify progressively higher elevations.

While spot heights and contour lines identify the precise elevations of precise locations, shadings refer to a range of elevations over an area. Thus, the lightest gray tone on Figure 5-3b signifies land that is anywhere between sea level and 100 feet above sea level.

Tip

But that’s just this one map. On a different map, the same gray tones may mean something very different. Similarly, a light brown color may signify a particular elevation on one map, but a very different elevation on a different map. Remember: Always check the legend to make sure of the meaning of particular shades.

Using Symbols to Tell the Story

As highlighted by the discussion of topography, maps commonly show things by means of point, line, and/or area symbols. Each category, in turn, may display either qualitative or quantitative information. That is, each can simply show where something is located, or how much of something exists at a particular location or over a particular area.

Point symbols

Point symbols are used to locate discreet phenomena on Earth’s surface. Most fall within one or more of the following categories.

bulletNominal icons are tiny likenesses or symbols they name (hence, nominal) and indicate the locations of particular landscape features. Thus a tiny black dot (•) may be used to symbolize a residence while a cross (†) may be used to locate a cemetery. Whatever the symbol, the cartographer must explain its meaning in the map’s legend.

bulletOrdinal icons are very much like nominal icons except that they come in different sizes that suggest comparable size or order (hence, ordinal). On some maps, for example, a tiny airplane might be used to symbolize a small airport, while a larger airplane is used to indicate a major airport. Similarly, a lower case u might be used to pinpoint a minor uranium deposit while a capital U locates a major one.

bulletDots are often used to show how the distribution of something varies numerically from place to place. Thus, for example, a map showing the geography of dairy cattle might use a series of dots, each one representing, say, 100 head of cattle. Similarly, a map of tobacco farming might use a series of dots, each representing, say, 100 acres of land in cultivation.

bulletProportional symbols vary in size in direct relation to numerical values. Thus, circles whose areas are proportional to population may indicate the locations and sizes of cities (Figure 5-4).

Line symbols

A number of important features on Earth’s surface are linear in nature, meaning they look like lines, such as roads or railways. Likewise, migration, travel, trade, and other movements of interest to geography are basically linear phenomena that connect points. Accordingly, line symbols are common features on maps and take one of the following forms.

bulletNominal lines note the locations of particular linear features, such as roads, railways, rivers, and borders. They may appear as solid, dashed, or embellished lines, the standard symbol for railroads being an example of the latter. Colors may also be employed. Blue lines, for example, are commonly used to indicate rivers.

bulletOrdinal lines vary in thickness or color to indicate relative importance. On many maps, for example, city, state, and country boundaries are progressively thicker so as to indicate the relative importance of the political units they mark. In Figure 5-4, the line that separates the United States and Canada is thicker than the lines that separate the states and provinces. Similarly, lines that symbolize roads often vary in thickness in proportion to the width of the highway or number of lanes.

bulletFlow lines indicate movement, travel or trade along a given route or between two points. On some maps, the thickness of the lines varies in direct proportion to the quantity or volume of the flow. Thus, on a map of immigration, arrows of varying widths may be used to indicate the volume of movement between sender and receiver regions (as shown in Figure 5-5).

bulletIsolines connect points of equal value with respect to a certain phenomenon. The contour lines shown in Figure 5-3b are an example. Similarly, daily weather maps often contain isolines that connect points with identical atmospheric pressure or the day’s projected high temperature.

Area symbols

Area symbols use gray tones or colors to depict phenomena that characterize areas as opposed to points or lines and are separated into two basic varieties.

bulletNominal symbols identify qualitative characteristics or phenomena that pertain to areas or regions. Figure 5-6, for example, uses nominal symbols to identify official languages of South American countries. Similarly, in Chapter 10 you encounter a series of maps that use nominal area symbols to identify the geographies of the world’s climate-types.

bulletChoropleth maps (from the Greek choros and pleth, meaning place and value respectively) use colors or gray tones to show how the quantity or numerical value of something varies from one area to the next. Figure 5-3c, which uses gray tones to depict elevations on an island, is an example.

Gathering Information: Sources for Pinpointing Objects

Few things are more important in cartography than the positional accuracy of mapped objects. Historically, this was accomplished by field observation. That is, explorers or surveyors would travel to a particular area, observe locally important features, and map their locations.

JargonAlert

Nowadays, GPS technology has greatly contributed to positional accuracy (see Chapter 3). In addition, many maps and the things that they show are products of remote sensing. In techno-speak, this refers to gathering information from afar about the Earth. In everyday English, it refers to use of aircraft and satellites to take pictures and picture-like images of Earth.

Aerial photography

Aerial photography refers to photos of Earth’s surface taken from aircraft. Today a majority of maps produced under government approval at all levels, municipal through federal, are directly derived from aerial photography. Black and white film has been a widely used medium (see Figure 5-7). In addition to being inexpensive, it generally provides a clearer view of Earth’s surface than does color film, and therefore makes it easier to identify and map surface features.

Infrared photography is also very popular. Infrared energy is contained in the sunlight that strikes the Earth and reflects off its surface. You and I can’t see it, but special kinds of films and sensors can. Infrared energy readily passes through haze and air pollution, resulting in crisp images even on days when the atmosphere is far from clean. Because of that very desirable characteristic, infrared photography is widely used in aerial surveys.

The gray tones and colors on an infrared photograph may be very different than those observed on regular black and white or color film. Because of that, the term false color is widely applied to infrared film and photographs. Most bizarrely, vegetation appears red. Indeed, the more lush or healthy the vegetation, which appears downright green to you and me, the redder it appears on an infrared photo. Infrared photos are capable of providing information that may not be apparent on normal color or black and white photos. For example, differences in redness may indicate different kinds of crops or forests, or indicate plant life that is stressed because of disease or drought.

Non-photographic imagery

TechnicalStuff

Like infrared photography, other remote sensing technologies record surface features in ways that are beyond the capabilities of human eyesight and normal cameras and film. Virtually all of them make use of sensors that scan the Earth and record surface information electronically. Because they do not use film, the pictures they produce are not, technically speaking, photographs. Thus, in the lingo of remote sensing, you have aerial photographs and non-photographic images. Three image-types are widely used.

bulletRadar imaging: In radar imaging, a sensor emits continuous beams of energy that bounce off Earth and return to the sensor, which records them. Because the emitted beams travel at a known and uniform speed, the time that it takes them to make the round trip is a function of the elevations of the locations where the beams reflect. For example, a beam that bounces off a mountaintop takes less time to return to the sensor than one that reflects off a valley bottom. This information can be used to produce detailed images of terrain and very exact topographic maps.

Radar beams can penetrate clouds and fog with no loss of strength. Thus, radar imaging is extremely useful for monitoring and mapping Earth’s surface in regions where atmospheric characteristics inhibit aerial photography (such as characteristically cloudy equatorial areas). It may also be used at night to the same effect as day. The same, of course, cannot be said of regular film.

bulletInfrared imaging: Infrared pictures of Earth may be obtained from scanners as well as films. Other than a different way of receiving images, the basic characteristics and use of infrared imaging is the same as for infrared films, discussed previously.

bulletThermal imaging: Thermal scanners (a form of infrared imaging) record heat differences on Earth’s surface. This is particularly useful for mapping ocean surface currents (whose temperature variations have a major effect on weather and climate) as well as for identifying and mapping different kinds of pollution. It has also proved very useful in mapping and monitoring forest fires and other fire-related phenomena, especially in situations in which smoke prohibits analysis by means of standard photography.

Applied Geography: The September 11th aftermath

In the aftermath of the terrorist attack on the World Trade Center, fires beneath the rubble posed significant problems for relief and rescue workers. In addition to the smoke and fumes, ongoing combustion progressively destabilized the huge debris piles in different places, heightening the danger to people on the scene. Thus, it was a matter of some importance to map the locations and intensity of “hot spots.” As a result, within 48 hours of the incident, a special aerial survey was conducted that included thermal imaging. The resulting data were used to produce maps that helped on-site commanders decide where to concentrate and where not to concentrate their personnel and fire-fighting assets.

Satellite monitoring

Numerous satellites monitor and provide map-ready information about Earth’s surface and atmosphere. Virtually all of them utilize non-photographic scanners that produce thermal, infrared, or radar imagery. Data received by the scanners are stored onboard the satellite for later transmission to receiver stations on the ground. There the information is processed and assembled into photo-like images (see Figure 5-8).

Getting Computerized

Today nearly all cartography at the professional level is done on a computer. Maps in this book are examples. Special kinds of software are available that allow cartographers to make maps with a degree of speed, accuracy, and data management that were unimaginable a few years ago. These qualities have also served to make mapmaking a powerful tool for a variety of businesses and planners. And in that regard, the most significant, cutting-edge field in contemporary cartography is the geographical information system (GIS).

Giving you the complete lowdown on GIS would involve a lot of techo-babble that you don’t want to read and I don’t want to write. So perhaps the best way for me to describe GIS begins with a description of what it has replaced.

If you had poked around a city or regional planning office 20 years ago, you’d be sure to find a huge table someplace with a huge base map that showed the streets and roads of the city or region in question. There would also be numerous overlays of different phenomena drafted on individual pieces of transparent film. For example, one transparent overlay might show the location of property boundaries. Others might show land use, sewage pipes, water mains, building characteristics, telephone lines, school districts, voting precincts, contour lines, wooded areas, and anything else that may be deemed useful for planning purposes.

Again, each characteristic would be on its own piece of transparent film — that is, its own map. So if a planner wanted to see how two phenomena coincided geographically, the respective transparent films would be manually overlain on the base map and comparisons manually noted. Of course, the landscape changes. Thus, every so often a particular overlay would have to be manually updated or manually redrafted from scratch. If all of this sounds a bit tedious, then you get the point.

With the advent of GIS, all of those physical base maps and pieces of transparent film have been replaced by layers of information that exist in computer memory. This permits multiple layers, or even parts of layers, to be compared electronically, which is to say instantaneously. But the bottom line is that GIS has given geographers and planners the power to map and compare phenomena with great speed and accuracy. Indeed, remotely-sensed images can be directly “fed into” a GIS, reducing to minutes and seconds a process of field observation and mapping that used to take weeks and months.

Does this electronic gadgetry mean that the romance and adventure of maps are gone? Not necessarily. Nearly everyday I see students gawking at maps, just as I did. True, the maps they are staring at are on a computer screen instead of the pages of a book, and are more likely to be products of remote sensing instead of expedition. But the intense fascination on peoples’ faces is palpable, so the old magic must still be there — the same old symbols certainly are — gray tones, different colors, tiny airplanes, and crosses. Some things don’t seem to change.

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