A map can be defined as a graphic representation of the real world. Because of the infinite nature of our universe, it is impossible to capture all the complexity in the real world. For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of the paper.

Maps are used to display both cultural and physical features of the environment. Standard topographic maps, also called reference maps, show various information, including roads, land-use classification, elevation, rivers and other water bodies, political boundaries, and the identification of houses and different types of buildings. With the growth of GIS, thematic maps are becoming quite common. As the name implies, thematic maps focus on a particular theme, such as U.S. Census data, COVID-19 cases, and deaths, shifting temperatures because of climate change, biodiversity hotspots, or loss, which are just examples. Esri has created a new commons database called The Living Atlas, allowing GIS users to upload dynamic maps into a “living atlas of the world.”

Great and Small Circles

Much of Earth’s grid system is based on the location of the North Pole, South Pole, and the Equator. The poles are an imaginary line running from the axis of Earth’s rotation. The Plane of the Equator is an imaginary horizontal line that cuts the Earth into two halves. This brings up the topic of great and small circles. A great circle is any circle that divides the Earth into a circumference of two halves. It is also the largest circle that can be drawn on a sphere. The line connecting points along a great circle is also the shortest distance between those two points.

Examples of great circles include the Equator, all lines of longitude, the line that divides the Earth into day and night called the circle of illumination, and the plane of the ecliptic, which divides the Earth into equal halves along the Equator. Small circles are circles that cut the Earth but not into equal halves. All lines of latitude, except the Equator, are made up of small circles.

Time Zones

Before the late nineteenth century, timekeeping was primarily a local phenomenon. Each town would set its clocks according to the motions of the Sun. For example, the Sun reached its maximum altitude above the horizon at noon. Cities and towns would assign a clockmaker to calibrate a town clock to these solar motions. This town clock would represent “official” time, and the citizens would set their watches and clocks accordingly.

The latter half of the nineteenth century was a time of increased movement of humans. Many people were moving west in the United States and Canada, and settlements in these areas began expanding rapidly. Railroads moved people and resources between cities and towns to support these new settlements. However, the railroads experienced significant problems constructing timetables for the multiple stops because of how local time was kept. Timetables could only become more efficient if the towns and cities adopted some standard method of keeping time.

In 1878, Canadian Sir Sanford Fleming suggested a system of worldwide time zones that would simplify the keeping of time across the Earth. Fleming proposed dividing the globe into twenty-four time zones, every 15 degrees of longitude in width. Since the world rotates once every 24 hours on its axis and has 360 degrees of longitude, each hour of Earth’s rotation represents 15 degrees of longitude.

Railroad companies in Canada and the United States began using Fleming’s time zones in 1883. In 1884, an International Prime Meridian Conference was held in Washington D.C. to adopt the standardized timekeeping method and determine the prime Meridian’s location. Conference members agreed that the longitude of Greenwich, England, would become zero degrees longitude and established the twenty-four time zones relative to the Prime Meridian. It was also proposed that the time measurement on the Earth would be made relative to the astronomical measurements at the Royal Observatory at Greenwich. This time standard was called Greenwich Mean Time (GMT).

Today, many nations operate on variations of the time zones suggested by Sir Fleming. This system measures time in the various zones relative to the Coordinated Universal Time (UTC) standard at the Prime Meridian. Coordinated Universal Time became the standard legal reference of time worldwide in 1972. UTC is determined from atomic clocks coordinated by the International Bureau of Weights and Measures (BIPM) in France. The numbers at the bottom of the time zone map indicate how long each zone is earlier (negative sign) or later (positive sign) than the Coordinated Universal Time standard. Also, note that national boundaries and political matters influence the shape of the time zone boundaries. For example, China uses a single time zone (eight hours ahead of Coordinated Universal Time) instead of five different time zones.

Geographic Coordinate Systems

Two types of coordinate systems are currently widely used in geography: the geographical coordinate system and the rectangular (also called Cartesian) coordinate system. The geographic coordinate system measures location from only two values, even though the locations are described for a three-dimensional surface. The two values that define location are measured relative to the Earth’s polar axis. The two measures used in the geographic coordinate system are latitude and longitude.

Latitude and Longitude

Latitude is an angular measurement north or south of the Equator relative to a point found at the center of the Earth. This central point is also on the Earth’s rotational or polar axis. The Equator is the starting point for the measurement of latitude. The Equator has a value of zero degrees. A line of latitude or parallel of 30° North has an angle of 30° north of the plane represented by the Equator. The maximum latitude value can attain 90° North or South. These lines of latitude run parallel to the rotational axis of the Earth.

Lines connecting points of the same latitude, called parallels, have parallel lines. The only parallel that is also a great circle is the Equator. All other parallels are small circles. The following are the essential parallel lines:

• Equator, 0 degrees
• Tropic of Cancer, 23.5 degrees N
• Tropic of Capricorn, 23.5 degrees S
• Arctic Circle, 66.5 degrees N
• Antarctic Circle, 66.5 degrees S
• North Pole, 90 degrees N (infinitely small circle)
• South Pole, 90 degrees S (infinitely small circle)

Longitude is the angular measurement east and West of the Prime Meridian. Lines connecting points of the same longitude are called meridians. The position of the Prime Meridian was determined by international agreement to be in line with the location of the former astronomical observatory at Greenwich, England. Because the Earth’s circumference is like a circle, it was decided to measure longitude in degrees. The number of degrees found in a circle is 360. The Prime Meridian has a value of zero degrees. A line of longitude or Meridian of 45° West has an angle of 45° west of the plane represented by the Prime Meridian. The maximum value that a meridian of longitude can have is 180°, the distance halfway around a circle. This meridian is called the International Date Line. The line determines where the new day begins in the world. Because of this, the International Date Line is not a straight line; it follows national borders so that a country is not divided into two separate days.

When parallel and meridian lines are combined, a geographic grid system allows users to determine their exact location on the planet.

Coordinate Systems and Map Projections

Depicting the Earth’s three-dimensional surface on a two-dimensional map creates various distortions involving distance, area, and direction. It is possible to develop equidistant maps. However, even these types of maps have some form of distance distortion. Equidistance maps can only control distortion along either latitude or longitude. Distance is often correct on equidistance maps only in the direction of latitude.

Distance distortion is usually insignificant on a map with a large scale, 1:125,000 or larger. An example of a large-scale map is a standard topographic map. On these maps, measuring straight-line distance is simple. Distance is first measured on the map using a ruler. Then, the map’s scale converts this measurement into a real-world distance. For example, if we measured ten centimeters on a map with a scale of 1:10,000, we would multiply 10 (distance) by 10,000 (scale). Thus, the actual distance in the real world would be 100,000 centimeters.

Measuring distance along map features that are not straight is more complicated. One technique employed for this task is to use several straight-line segments. This method’s accuracy depends on the number of straight-line segments used. Another method for measuring curvilinear map distances is to use a mechanical device called an opisometer. This device uses a small rotating wheel that records the distance traveled. The recorded distance is measured by this device either in centimeters or inches.

Historically, most maps were hand-drawn, but with the advent of computer technology, more advanced maps were created with satellite technology. Geographic information science (GIS), called geographic information systems, uses computers and satellite imagery to capture, store, manipulate, analyze, manage, and present spatial data. GIS primarily uses layers of information and is often used to make decisions in various contexts. For example, an urban planner might use GIS to determine the best location for a new fire station, while a biologist might use GIS to map the migratory paths of birds. In addition, we use GIS to get navigation directions from one place to another, layering place names, buildings, and roads.

One difficulty with map-making is that the Earth is a sphere, while maps are flat even with advanced technology. As a result, some distortion always occurs when converting the spherical Earth to a flat map. A map projection, or a representation of Earth’s surface on a flat plane, always distorts at least one of these four properties: area, shape, distance, and direction. Some maps preserve three of these properties while significantly distorting another, while other maps seek to minimize overall distortion but distort each property. So, which map projection is best? That depends on the purpose of the map. For example, while significantly distorting the size of places near the poles, the Mercator Projection preserves angles and shapes, making it ideal for navigation. The Winkel Tripel Projection is so named because its creator, Oswald Winkel, sought to minimize three kinds of distortion: area, direction, and distance. The National Geographic Society has used it since 1998 as the standard projection of world maps.