Map

• 1. Introduction

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  The word "map" began as a napkin. It comes from the Latin phrase Mappa mundi, where mappa meant a napkin or cloth and mundi meant "of the world." Over time the phrase shrank to a single syllable, naming any flat representation of the Earth's surface. That humble origin hides a strange truth. A map is a depiction of interrelationships, commonly spatial, between things within a space. It need not show geography at all. It can represent any space, real or fictional, two-dimensional like Earth's surface or three-dimensional like Earth's interior. Maps appeared in several societies before those same societies had written communication systems. The earliest surviving examples are cave paintings and etchings on tusk and stone. So how did a cloth-named sketch become an instrument of empire, a tool of disease detectives, and a thing that nations jail people for drawing wrong? And why can no flat map of our round planet ever tell the whole truth? The answers run from ancient Babylon to a 70-ton sculpture of Scotland.

• 2. The Distortion Problem

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  Flattening a sphere onto a plane is impossible without distortion, and that single fact shapes everything about how maps work. Geographic maps use a projection to translate the three-dimensional surface of the geoid into a two-dimensional picture, and projection always distorts. There are many ways to apportion that distortion, so there are many projections, and which one to choose depends on the map's purpose. The Mercator Projection, developed by the Flemish geographer Gerardus Mercator, served as the standard for two-dimensional world maps until the late 20th century. More accurate projections then came into wider use. Mercator left a second legacy too. He was the first to use and popularize the concept of the atlas, a collection of maps. Distortion also breaks the simple idea of scale. Many maps state a scale as a ratio such as 1:10,000, meaning one unit on the map equals 10,000 of that unit on the ground. That statement holds when the region is small enough to ignore the Earth's curvature, like a city map. Across a world map, scale as a single number is practically meaningless, and it usually refers only to the scale along the equator. The best most projections can manage is an accurate scale along one or two paths.

• 3. Which Way Is Up

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  North at the top of a map is a convention only a few hundred years old. On a spheroidal planet no direction is inherently "up," so mapmakers across history have chosen many orientations. In the Middle Ages many Eurasian maps, including the T and O maps, were drawn with east at the top. The word "orient" itself comes from the Latin oriens, meaning east. The reasons for these choices were often sacred. European Christian maps like the T-O map placed east at the top because that was the direction of the Garden of Eden. Early Islamic maps often put south at the top because Mecca lay south of the map-makers. Early Chinese maps placed north at the top because that was the location of the imperial capital, even though most Chinese compasses pointed south. Practical and cultural factors bent orientation in other directions still. In the Northern Hemisphere, north and west were historically kept off the top because those were the directions where the sun disappeared. Portolan charts face the shores they describe. Maps of cities beside a sea often put the water at the top. Polar maps center on the pole, with North pointing toward or away from the middle. Ancient Egyptians used a south-up orientation, and some maps in Brazil still do today. Buckminster Fuller's Dymaxion maps project the sphere onto an icosahedron, whose triangular pieces can be arranged in any order at all.

• 4. Useful Lies

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  The famous London Underground map respects the city's geographic structure but smooths the tube lines and the River Thames to clarify the relationships between stations. Near the center, stations sit farther apart than they do near the edges. This is deliberate inaccuracy in the service of clarity, and it is everywhere in cartography. Cartograms take the idea further, distorting scale on purpose to reflect information other than land area or distance. A road map may quietly omit railroads, smaller waterways, or other prominent non-road features, or render them as faint dashed lines so the roads stand out. This practice, known as decluttering, makes the subject easier to read without sacrificing overall accuracy. Some omissions serve secrecy rather than design, as when cartographers leave military installations off the map entirely. Scholars of critical geography, including John Brian Harley, argue that all maps are charged with rhetorical biases and should be viewed with skepticism. A map can change or enforce a view of a place by shifting the viewer's perspective. Americans long believed the Atlantic and Pacific Oceans insulated them from European conflicts, until aviation maps highlighted how close North America and Europe sit across the North Pole. That realization helped spawn an entire study of how maps alter human perspectives of the globe.

• 5. The Cartographer's Craft

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  From clay tablets to geographic information systems, the design and production of maps is a craft that has developed over thousands of years. The person who makes a map is called a cartographer or mapmaker, and cartography is the study and practice of crafting representations of the Earth on a flat surface. The work is closer to graphic design than most people expect. A good map integrates scientific knowledge about how maps are used with principles of artistic expression, aiming for a product that is attractive, carries an aura of authority, and serves its intended audience. Designing one means juggling several elements at once in an iterative feedback process rather than finishing each in turn. Generalization is the discipline of choosing what to leave out, since every map shows only a tiny sample of the information about a place, adjusted to fit the scale and purpose. Symbology represents features through visual variables like size, shape, color, and pattern, and those symbols are usually explained in a legend on the margin or on a separate characteristic sheet. Composition governs how symbols interact through grouping and visual hierarchy, while typography positions the labels that help readers recognize features. Some cartographers fill the entire sheet with the map, tucking the title, compass rose, and bar scale into a blank "inside" region called a cartouche. They may also inset smaller maps, the way Alaska and Hawaii ride along the edge of a map of the United States, or the Shetland and Orkney Islands sit beside a map of Britain.

• 6. Maps That Found Cholera

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  In the pre-electronic age, layering data onto a map led Dr. John Snow to identify the location of a cholera outbreak. That act of superimposition foreshadowed the modern tool that now dominates the field. Since the last quarter of the 20th century, the computer has been the cartographer's indispensable instrument, and much of map-making, especially at the survey level, has been absorbed by geographic information systems, or GIS. GIS makes it simple to lay variables such as rainfall level, wildlife distribution, or demographic data over an existing geographic map, which sharpens analysis and decision-making for users as diverse as wildlife conservationists and militaries. Interactive computerized maps let users zoom in and out, sometimes by swapping one map for another at a different scale centered on the same point. In-car global navigation satellite systems are computerized maps with route planning that track a user's position using satellites. Beneath the surface, zooming carries surprising subtlety. It can mean replacing a map with a more detailed one, enlarging the same map without enlarging the pixels, or enlarging the pixels themselves. A vector format such as a PDF can be enlarged until a curve resolves into straight lines, arcs of circles, or splines. A map may even mix layers that are partly raster graphics and partly vector graphics, with text that does not necessarily grow as you zoom in.

• 7. Mapping Climate And Beyond

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  Isotherms connect points of equal temperature, isobars connect points of equal pressure, and isohyets connect points of equal precipitation. These isolines are the language of climatic maps, which reflect the territorial distribution of climatic conditions from long-term observation. The vocabulary runs deeper still. Isoamplitudes trace amplitudes such as the annual difference between the warmest and coldest months. Isanomals trace anomalies, like how far a place departs from the mean temperature of its whole latitudinal zone. Isochrones mark the dates a phenomenon begins, such as the first frost or the appearance of snow cover. Climatic maps generally apply to individual months and the year as a whole, sometimes to the four seasons or the growing period. Where there are no measurements, spatial interpolation synthesizes values, assuming conditions change smoothly. Maps reach far past climate and Earth. They exist of the Solar System, of star fields, and of bodies like the Moon and other planets, which are technically not geographical maps at all. Topological maps abandon geography entirely, preserving only connectivity, the way schematic diagrams, Gantt charts, and subway maps show logical rather than spatial relationships. Road maps remain perhaps the most widely used today, one subset of navigational maps alongside aeronautical and nautical charts. Yet the largest number of drawn map sheets probably comes from local surveys carried out by municipalities, utilities, tax assessors, and emergency services.

• 8. Giants And Borders

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  The Great Polish Map of Scotland weighs 70 tons. Polish general Stanisław Maczek had been shown an outdoor map in the Netherlands that demonstrated the working of waterways, an obstacle to Polish forces in 1944. The sight inspired him and his companions to build a permanent three-dimensional thank-you for Scotland's hospitality to his compatriots. In 1974 a Polish student geographer-planner, Kazimierz Trafas, laid out the coastline and relief from existing Bartholomew Half-Inch map sheets, and at the general's request some main rivers were arranged to flow from headwaters pumped into the mountains. Finished in 1979, the map had to be restored between 2013 and 2017. Other giants share its ambition. The Challenger Relief Map of British Columbia, hand-built by George Challenger and his family from 1947 to 1954, measures 80 feet by 76 feet and occupies 6,080 square feet, which the Guinness Book of Records cites as the largest of its kind in the world. It drew millions of visitors at the Pacific National Exhibition in Vancouver from 1954 to 1997. Francisco Vela's relief map of Guatemala, made in 1905 to educate children about their country, still measures 1,800 square meters. Maps can also carry the force of law. Within Russia, Google Maps shows Crimea as part of Russia. India and China each require maps to show the Sino-Indian border dispute in their own favor. In Pakistan, the Surveying and Mapping Amendment Act of 2020 made using an "incorrect" map of Pakistan a crime punishable by 5 years in jail and a fine of 5 million rupees.