Geographical Education

(Note: This is the final post in a long series on basic physical geography, which was originally designed to help educators teach the subject. As the series progressed, however, posts have strayed outside the pedagogical realm. I do hope to return eventually to the original project and write more short essays on the fundamentals of global climatology, landforms, biogeography, and so. But for the time being, I am eager to move on to other topics.)

As I have been harshly critical of latitude-based climate maps, it is only fitting to offer an alternative, which can be found below. Note that I do not label this scheme as a “climate map,” but instead return to the ancient Greek term “clime.” A clime is closely related to a climate zone but is not the same, as it based strictly on latitude, ignoring the other factors that determine climate. As such, it could be described as an “Earth-sun relations map,” one that mostly indicates zones of seasonally changing sun angles and day lengths.

This is an admittedly an idiosyncratic map, as it reflects my own perspective that insists on differentiating climate zones from climes. As argued in a previous post, I reject the conventional definition of the “subtropics” as extending to 35° or even 40° latitude, as it encompasses vast swaths of land that regularly experience severe cold, precluding subtropical vegetation. I also find it unreasonable to place well over half of the world’s landmass in zones that use the term “topic” in their labels [1]. Such a scheme also unduly restricts the temperate belts. The subarctic zone, according to the Wikipedia article on the topic, can extend as far toward the Equator as 50° latitude. This definition is true in a climatic sense [2]. But if such a latitudinal delineation of the subarctic zone is used in combination with the maximal definition of the subtropical zone, the temperate belts would be restricted to a mere ten degrees of latitude north and south of the Equator (40° to 50°).

A few additional explanatory notes are needed for my map of climes. Following the standard convention, my tropical zone extends from 23.4° N to 23.4° S. Within this belt, between 5° N and 5° S, I have added an equatorial sub-zone. I differentiate the equatorial latitudes because they experience high sun angles at midday throughout the year, unlike the outer tropics. More significant is the fact that tropical cyclones are unknown in the equatorial belt, due to the absence of spin provided by the Coriolis pseudo-force, as can be seen in the map posted below.

Following the norm, I have delineated subtropical zones on the poleward sides of the tropics, but I have unconventionally restricted them to 30° latitude. I do this partly to match the common perception of the term “subtropics” in the United States, but mostly because I think that zones conceptualized in terms of adjacent zones should be relatively narrow. The admittedly arbitrary 30° limit was chosen mostly because it is a round number that is easy to remember.

Broad mid-latitude zones are found on my map between 30° and 60° north and south of the Equator. This definition puts the midlatitudes in the same general angular range as the two other primary climes: the tropical and arctic/antarctic zones (a 30° span for each midlatitude zone, a 46.8° span for the tropical zone, and a 23.6° span for each “arctic” zone). Because my midlatitude belts are so wide, I have subdivided them into inner (toward the Equator) and outer (toward the poles) zones. The division line is placed at 45° N & S, the latitude halfway between the poles and the Equator.

My subarctic and subantarctic zones follow the same general logic used for my subtropical zones. They are thus mapped as extending between the arctic/antarctic circles and 60° N & S.

Finally, following standard conventions, I have designated arctic and antarctic zones as extending from the poles to the arctic and antarctic circles. In both cases, I have distinguished polar subzones at latitudes higher than 80°. Here the midday sun angle is always low and most of the year is characterized by either continual daylight or continual night.

[1] ChatGPT tells me, that “Some geography-climate sources suggest that the “tropical + subtropical” belt (which roughly approximates 40° S to 40° N, depending on definition) includes a substantial majority of Earth’s land. For example — although exact slicing by latitude is more complex — one review of land-area distributions finds that when land is mapped by latitudinal bands, the tropical and near-tropical bands dominate global land area.”

[2]. In the Southern Hemosphere, subarctic climates extend into latitudes lower than 50°. In the Kerguelen Islands, at 49° S, the daily mean temperature in the warmest month is a chilly 8.6° F (47.5° C), which, according to the Köppen climate classification system, makes it a “tundra climate.”

In searching the internet for climate maps that might be useful for educational purposes, I have continued to be disappointed and occasionally dumbfounded. Many highly ranked maps provide outright misinformation. Consider, for example, the two maps posted below, both of which divide the world into climate zones based simply on latitude. As explained in previous posts, this expedient is problematic, although can be useful in certain circumstances. But these two maps make the inexcusable error of labeling the subtropics as “dry climates.” (The two maps might seem to have identical content, but they differ slightly, as the first puts the outer limit of the northern subtropical “dry” zone at 35° N, the most common definition, whereas the second puts it at 37° N.)

Although the belts of land between 23.4° and 35° north and south of the Equator do contain the world’s most extensive arid areas, and some of its driest ones, they also encompass extensive humid areas, as well as some of the wettest places on Earth. The difference is whether they are located on dry western sides of major landmasses or on the wet eastern sides – with Eurasia and North Africa forming a single landmass, or continent, in climatological terms. This distinction is easily seen on the map posted below, especially in the northern subtropics. As the call-out that I added indicates, the only area in its hyper-wet purple category, with more than 7475 millimeters (294.4 inches) of annual average precipitation, is found in this zone. Although it is almost impossible to see, a small blue area with even more rainfall is located in the same general area (note that the map key is slightly mislabeled, as the “10005” and “394.0” figures should be in the left-hand columns).

This extremely wet area in a reportedly dry climate zone is the southern part of the small state of Meghalaya in northeastern India. Here the town of Cherrapunji (or Sohra), at 26° N and 4,690 ft (1,430 m), is often regarded as the “wettest place on planet Earth,” although the nearby village of Mawsynram might be even wetter. This title, moreover, is also disputed with Mount Waiʻaleʻale on the island of Kauaʻi in Hawaii and the town of Lloró in northwestern Colombia, as was explained in an old GeoCurrents post. As that post noted, it may be impossible to determine what specific place receives the most annual precipitation. But in terms of reliably heavy precipitation throughout the year over a sizable area, northwestern Colombia does rank in first place.

As noted in the previous post, many educational climate maps that rank high in internet image searches are based on a simplistic climatic model that is too focused on latitude. In this post, I scrutinize and criticize four such maps.

The most simplistic example that I found (posted below) essentially replicates Aristotle’s five-zone climate scheme, although it does not strictly follow latitudinal lines. The marginal notes on this STUDYLIB map claim that the climate zones that it depicts are based on both average temperature and average rainfall, but that is simply not the case. While the text states that the tropical zones “get the most rainfall,” the map puts the world’s largest hyper-arid area, the Sahara Desert, in this category. While the text states that the temperate zones experience “rainfall year-round,” the map puts many place that almost never get summer precipitation in this category. While the text states that the polar zones are “almost always below freezing,” the map puts relatively mild Iceland and the Alaska Peninsula along with the nearby Aleutian islands [1] in this category. Perhaps surprisingly, neither Reykjavík in Iceland nor Dutch Harbor in Alaska have a single month with a daily mean temperature below freezing. (The figure for the coldest month in Reykjavík [February] is 32.9°F/0.5° C, and for Dutch Harbor is 33.0°F/0.6° C.) Note also that the base map is extraordinarily crude, especially in its depiction of Southeast Asia.

The second map, produced by Larkswood Educational Supplies, is essentially the same as the first, although it adds two “Mediterranean” zones, one in California and the other in the Mediterranean itself. The addition of this dry-summer zone is an improvement, but the map fails to get the geography right. It is oddly missing the eastern Mediterranean and it ignores the Mediterranean-climate zones in central Chile, southwestern South Africa, and southwestern and south-central Australia. It also puts areas with non-Mediterranean climates, such the Po Valley of Italy and most of the Danube Basin, in the Mediterranean category.

The third map, produced by Dreamstime.com, has six climate zones. As such, it is an improvement over the first two, although, unlike the second, it fails to differentiate Mediterranean climates. Its miscues, however, are many. It places hyper-arid northwestern Peru [2], for example, in the equatorial zone, which is generally characterized by heavy rainfall over most of the year, yet it excludes most of hyper-wet western Colombia from the same category. It puts Irkutsk, Russia, with a mean January low temperature of -6.5°F/-21.4°C, in the temperate zone, yet it does the same with tropical Dhaka, Bangladesh [3], which a record low temperature of 42.1°F/5.6°C and an annual daily mean temperature of 78.8°F/26.0°C. The much colder city Shreveport, Louisiana, with a record low of -5.0°F/-21°C and an annual daily mean temperature of 66.6°F/19.2°C, is conversely placed in the subtropical zone. Such mapping makes no sense.

The final map is the worst, even though it differentiates the largest number of climate zones. It extends the temperate zone into absurdly high latitudes, including southern Greenland, central Alaska, and north-central Siberia. Even infamously frigid Verkhoyansk, Russia, with a record low of -90°F/-67.8°C and an annual daily mean of 7.3°F/-13.7°C, is mapped in the temperate category! Equally ludicrous is the placement of southern Alberta and the Altay Mountains of Central Asia in the subtropical zone and the placement of the Tibetan and Loess plateaus of China in the ostensibly warmer “subequatorial” zone. This map is nothing less than a climatological travesty.

Although it is perhaps unfair to ridicule such maps, I do think that their prominence in internet image searches is both telling and tragic. Geographical knowledge has reached such a low state that even people tasked with producing and reviewing basic educational maps are unable to get fundamental facts right. We deserve better.

[1] Only one Aleutian island, Unimak, is actually depicted.

[2] The average annual precipitation in Chicalayo, Peru is 1.06 inches/26 mm.

[3] At 23°42’37” N latitude, Dhaka is just north of the Tropic of Cancer and thus just outside tropical zone strictly defined, but its climate is essentially tropical.

As the previous GeoCurrents post noted, longitude is to a significant extent a matter of time. Historically, every town kept its own time based on its longitude. Wherever you found yourself, “noon” was the moment when the sun reached its highest point, with the other hours of the day set around that time. Travelers reset their watches as they came into new towns if moving east or west, but there were no “time zones” as there are today. When railroads were developed in the mid-1800s, allowing much faster travel, local timekeeping made it almost impossible to schedule the arrival and departure of trains. In response, uniform time-zones were established at one-hour intervals.

The entire world was eventually divided into 24 time zones, one for each hour of the day. As there are 360° of longitude around the Earth (180° west and 180° east of the Prime Meridian), and as 360 divided by 24 is 15, geographical units of one hour of time are equivalent to swaths of 15° degrees of longitude. Modern time zones are thus theoretically centered on lines of longitude in multiples of 15 (15°, 30°, 45°, 60° and so on), extending 7.5° to the east and west of those central meridians.

But as can be seen on the first map posted below, time zones are only structured this way in the uninhabited polar regions. Everywhere else, geopolitical considerations intrude. On land, time zones almost never follow the lines of longitude on which they are ideally based. Even in the open ocean, they often deviate from them to group islands and archipelagoes with other places. In the north Atlantic, for example, Jan Mayen is in the time zone commonly called GMT +1* (one hour ahead of Greenwich Mean Time), whereas by the logic of longitude it would be in time zone GMT -1 (one hour behind of Greenwich Mean Time). Not surprisingly, Jan Mayen is in the same time zone as Norway, the country that controls it. But note that western Norway would be in a different time zone (GMT 0) if longitude were the only factor.

Some time zones almost disappear over continental landmasses, and where they do appear they can stray outside their ostensible longitudinal bounds. As can be seen in the map posted below, GMT+4 and GMT+6 (formally, UTC+04:00 and UTC+06:00) are prime examples. The only countries in GMT+4 that fit its longitudinal definition are Oman, the United Arab Emirates, Mauritius, and a small part Russia; Georgia, Armenia, Azerbaijan, and the Seychelles are also in GMT+4, but they are located outside its formal longitudinal range. GMT+6 has a similar geography. Bangladesh and Bhutan are the only countries using this time that are within its longitudinal bounds, while Kyrgyzstan and small piece of Russia also use it even though they are outside of its theoretical limits.

Many other major departures from the geometrical logic of 24 time zone, each based on 15° of longitude, can be seen on the global time-zone map. Most result from countries insisting on being on a single time zone regardless of their east/west span. India is a good example. By longitudinal logic, western and center India would be in GMT+5 (UTC+05:00), the same zone as Pakistan, while eastern India would be in GMT+6 (UTC+06:00), the same zone as Bangladesh. The Indian government opted to split the difference and put the whole country in the time zone officially designated as UTC+05:30. Nepal took this maneuver a step further, using GMT+5.45 for the whole country.

China is the extreme example of a country shoehorning a vast east/west span into a single time zone. China would extend over five time zones if it followed the strict longitudinal model. Instead, the whole country sets its clocks at GMT+8, using the time zone that is theoretically reserved for eastern China, the political and economic core of the country. As a result, in western China 12:00 PM, or “clock noon,” falls in the middle of the morning.

In the United States as well, time zones do not closely follow lines of longitude. Instead, they take into account state and county boundaries. One reason for these deviations is the inconvenience that would result from dividing extended metropolitan area into two time zones. In the U.S. west, for example, northern Idaho is on Pacific Time while much of eastern Oregon is on Mountain Time, even though northern Idaho is east of eastern Oregon. This arrangement makes sense because northern Idaho is oriented toward Spokane, Washington, which is on Pacific Time, while eastern Oregon is oriented toward Boise, Idaho, which is on Mountain Time.  But as can be seen on the map posted below, if time zones in the U.S. strictly followed the lines of longitude on which they are ostensibly based, both of these regions would be on Pacific Time.

*  More formally, this time zone is designated “UTC+00:00,” or “Coordinated Universal Time  00:00. ” As explained in a Wikipedia article on the subject:

UTC+00:00 is an identifier for a time offset from UTC of +00:00. This time zone is the basis of Coordinated Universal Time (UTC) and all other time zones are based on it. In ISO 8601, an example of the associated time would be written as 2069-01-01T12:12:34+00:00. It is also known by the following geographical or historical names:

• Greenwich Mean Time
• Western European Time
• Azores Summer Time
• Eastern Greenland Summer Time
• Western Sahara Standard Time
• Coordinated Universal Time

As was noted in an earlier post, most maps made in the 1500s and 1600s were relatively accurate in the north/south direction but often strikingly inaccurate in the east/west direction. This discrepancy was because latitude was relatively easy to determine (by the midday sun angle or by the position of the north star), whereas longitude could only be estimated. The inability to measure longitude led to countless shipwrecks, demanding a response. The problem was finally solved in the late 1700s by the development of better clocks.

Most students, in my experience, are surprised to learn that sturdy and accurate clocks allowed mariners to determine longitude. But whereas latitude is mainly a matter of sun angles, longitude is mainly a matter of time. Owing to the rotation of the Earth, places to the east of one’s own position are later in the day while places to the west are earlier. As modern travelers know, the time-disruption known as jetlag only occurs when one flies a long distance to the east or west, not to the north or south.

So how could an accurate clock sturdy enough to keep time on stormy seas allow navigators to plot longitude? The purpose of such “marine chronometers,” as they were called, was not to track local time, which was continually changing as one sailed to the east or west. Shipboard time could be set by observing when the sun reached its highest position, which marked noon. The ship’s chronometer, in contrast, indicated the time experienced at a different longitude, which was deemed 0°, or the “Prime Meridian.” As the chronometer was developed in Britain, those who first used the device designated the line of longitude passing through the British Royal Observatory in Greenwich, England as the Prime Meridian. At the International Meridian Conference, held in 1884 in Washington, D.C., representatives from 26 countries agreed to accept Greenwich as marking longitude 0°. Since then, its designation as the Prime Meridian has been essentially universal.*

The procedure for determining longitude by a chronometer set to the time in Greenwich was relatively simple. If the clock recorded that that it was midnight at Greenwich when it was noon on a ship, the vessel had to be on the opposite side of the world from the Prime Meridian, or Longitude 180°. If noon on the ship corresponded to 6:00 PM at Greenwich, the ship had to be at longitude 90°W, or one quarter the way around the world toward the west. By the same reasoning, if it was 6:00 AM at Greenwich when the local time was noon, the ship was one quarter the way around the world in the other direction, or at longitude 90° E.

The story of the development of the maritime chronometer and the determination of longitude is fascinating and instructive. It has been admirably told by writer Dava Sobel in her book Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time.

*France long resisted the designation of the line of longitude passing through Greenwich as the Prime Meridian as well as the global establishment of “Greenwich Mean Time.” France abstained on the vote in 1884 (as did Brazil, while the Dominican Republic voted against the measure). As noted in the Wikipedia article on the International Meridian Conference, “The French did not adopt the Greenwich meridian as the beginning of the universal day until 1911. Even then it refused to use the name “Greenwich”, instead using the term “Paris mean time, retarded by 9 minutes and 21 seconds”. France finally replaced this phrase with “Coordinated Universal Time” (UTC) in 1978.”

I had decided to move on from exploring the priority of north & south over east & west, but I realized that the most prominent example in the United States had escaped my attention: the northeast coast. Although this coast is often regarded as mostly oriented in a north/south direction, its actual orientation in more east to west. Boston, for example, is 114 miles north of New York City but 153 miles to its east. The situation is southeastern Massachusetts is more extreme. The town of Nantucket, for example, is 203 miles east of New York City but only 39 miles to its north. From New York to Cape Cod, the coastline runs almost west to east. Countering common expectations, moreover, New England is not north of New York state. If one excludes sparsely populated northern Maine and insular Long Island, New England is essentially due east of New York. While I imagine that this fact is widely understood locally, I have a strong suspicion that most Americans would find it surprising.

The misperception of Atlantic coastal orientation is heightened if one examines southeastern Canada together with northeastern U.S. together with. To the extent that Americans know about Nova Scotia, I think that it is safe to assume that most of them regard this Canadian province as located north of Maine. Actually, as can be seen in the map posted below, Nova Scotia is essentially due east of Maine. If this map appears to have misplaced these polities, examine the two maps posted below it, which reveal the larger regional context (and show how I made the first map).

This east-northeast coastal orientation extends as far as the island of Newfoundland. As can be seen on the map posted below, St. John’s is only 473 miles north of New York but 1,055 miles to its east. It is also much closer to London (2,285 miles) than it is to Vancouver (3,125 miles).

Because of its eastern location, Newfoundland was once a key refueling location for trans-Atlantic aviation. In the 1940s, Gander International Airport, 124 miles northeast of St. John’s, was one of the busiest airports in the world. Undermined by direct trans-Atlantic flights and far from any cities, Gander lost most of its traffic and now faces, according to Wikipedia, a “grim” future. The St. John’s airport, or Torbay as it is commonly called, has fared much better. According to one (overly?) optimistic local media outlet:

[Newfoundland’s] airports continue to serve as vital links for passengers, cargo, and emergency services, ensuring that the province remains well-connected to the rest of the world. As technology and travel continue to advance, Newfoundland’s skies will remain as busy as ever, carrying on its legacy as the gateway to North America.

As a final note, I suspect that misunderstandings of the directional orientation of the eastern coast of North America stem not just from perceptual issues also from geopolitical considerations reflected in mapping conventions. Maps made in the U.S. usually terminate at the border, with relatively few showing the geographical relationship between the northeast United States and southeast Canada. As can be seen in the figures posted below, image searches for “east coast North America map” mostly return maps limited to the east coast of the United States. Most that include southeastern Canada, moreover, are simple outline maps with little content. We deserve better.

Learning the cardinal directions is an important but often neglected aspect of early geographical education. It is my impression that the understanding of cardinal directions, like most other aspects of geography, is in sharp decline. There are several reasons for this regression, but surely one of the most important is the abandonment of map navigation in favor of following simple right-left instructions generated by automated mapping programs. If we are to revitalize geographical education, we should teach students about the cardinal directions at an early age.

It is usually best to begin such teaching at the local scale and then gradually expand the coverage. Start by giving young students a neighborhood map and then ask them to plot several courses to a familiar destination. Those courses can then be taken on foot while paying careful attention to the cardinal directions that one is following.

Obtaining maps at the appropriate scale can be a problem. My solution is to take a screenshot from Google Maps or Apple Maps, drop it into a presentation program like PowerPoint or Keynote, outline and highlight the features that I want to emphasize, and then delete the original map fragment. That may seem like a lot of work, but it is easily accomplished. An example that I made for my five-year-old granddaughter, with her own house in blue, is posted below. With this map in hand, we can walk to her friend’s houses, tracing our paths and noting the directions that we take. A compass can be used to verify these directions. I can also ask her to figure out what the colors and shapes on the map indicate (black for the main access road, dark grey for neighborhood streets, light grey for walking/biking paths, green for grassy areas, and polygons for houses and garages). In such a way, children can gain a deep understanding of both cardinal directions and mapping conventions.

More formal lessons on the cardinal directions can be conducted by observing the course of the sun over the day and marking its changing directions with a shadow-stick. A shadow-stick is simply a vertical pole fixed in the ground in a flat, sunny location. The spring and fall equinoxes are the ideal dates for such a lesson. If students can awaken early enough, they can observe the sun rising directly to the east, noting this direction on a neighborhood map. In the early morning, the shadow will be much longer than the pole and will point to the west, away from the sun. As the morning progresses, the shadow will swing toward the north and gradually shorten as the sun climbs. At midday, the shadow will point directly north, away from the sun. Over the afternoon, students can observe the shadow again lengthening but now swinging to the east. If the horizon is directly visible, they can see that when sunset approaches and is finally reached, the shadow becomes so long that it seemingly stretches to infinity and vanishes. Through such a lesson, both cardinal directions and sun angles can be explained and visualized.

As a more advanced lesson, students can be asked to use a shadow-stick to create a sun compass, which also functions most effectively on the equinoxes. At any time of the day, a rock or another vertical stick can be placed on the ground to mark where the shadow ends. After waiting some 20 minutes, another marker can be placed at the end of the shadow’s new position. After this process has been repeated a few times, another straight stick can be placed on the ground across these markers, which will indicate the east/west axis. Another stick perpendicular to the first will then indicate north and south. Many instructive YouTube videos on sun compasses are readily accessible.

The changing direction of the stick’s shadow over the course of the day can also be used to indicate time, although in a crude manner. Actual sundials are intricate devices, which are best covered at the secondary-school level. But a simple sundial of the sort illustrated below is still useful, especially on the equinoxes. It is also helpful for introducing the concept of longitude, which is to a significant extent a matter of time, as will be explored in the next few GeoCurrents posts.

Finally, in some areas local topography can be very useful for familiarizing young students with the cardinal directions. In the vicinity of Bozeman, Montana, for example, the prominent north/south trending Bridger Range is visible in most places, helping students orient themselves and visualize directions.

The cardinal directions seem to be equivalent concepts and certainly appear that way on maps and globes. Everywhere on Earth, one might assume, the north/south axis is perpendicular the east/west axis, with the four lines that indicate the cardinal directions meeting at right angles. Everywhere on Earth, or so it would seem, east is defined as the direction in which the sun rises, while west is defined as the direction in which it sets.

The actual situation, however, is more complicated. The cardinal directions, for example, collapse as you approach the poles. At the North Pole, all directions point “south,” while at the South Pole all directions point north. As can be seen in the diagram below, a few feet away from the North Pole the east/west directions, which follow latitude, form a tight curve, and thus do not meet the north/south axis at right angles. Daily sunrise and sunset, moreover, never occurs at the poles, as the sun remains above the horizon for half the year and below it for the other half. Equally significant, nowhere on Earth does the sun rise directly in the east or set directly in the west except at the two equinoxes (around March 20 and September 22). In the Northern Hemisphere’s midlatitude belt on the summer solstice (June 21), for example, the sun rises and sets well to the north of due east and west, while on the winter solstice it rises and sets well the south of the same directions. If its rising and setting positions are averaged out over the entire year, however, the sun does rise directly in the east and set directly in the west.

South and north can also be defined by the sun’s apparent position relative to the Earth. Throughout the contiguous United States (or “lower 48”), south is the direction of the sun when it reaches its highest position in the sky, halfway between sunrise and sunset, while the north is the opposite direction. But this definition only works in the midlatitude and arctic* belts of the Northern Hemisphere. In the corresponding zones of the Southern Hemisphere, the sun is located to the south when it reaches its highest position. In the tropics, in contrast, the midday sun is sometimes in the south and sometimes in the north, as has been explained in previous posts.

The crucial difference between the north/south directions and the east/west direction, however, is the absolute nature of the first pair and the relative nature of the second. North and south always and everywhere point to specific places, the north and south poles respectively (except at the poles themselves). East and West, on the other hand, are relative directions, as there is no easternmost or westernmost point on the planet. If you continue traveling straight to the east, you will eventually pass your starting point and find yourself to the west of it. From the global perspective, a given place can only be “west” or “east” relative to another place. The concept of “east” and “west” poles is absurd, although evidently enough people ask about them that detailed explanations are necessary (see the figure below).

This relativity of the east-west direction can generate geographical confusion. China, Japan, and Korea are sometimes called the “Far East” because they are located far to the east of Europe, where the term originated. But from the perspective of the western United States, they are in the far west. By the same token, people often become confused about the location of the eastern Pacific Ocean, thinking that it must be near East Asia, another name for the Far East. But it is the western Pacific that is next to East Asia, while the eastern Pacific is adjacent to the west coasts of North and South America.

Despite the relative nature of the east/west directions, east is always the general direction of sunrise (except at the highest latitudes), while west is always the general direction of sunset. And despite the absolute nature of the north/south direction, north and south indicate opposite orientations toward the sun in the northern and southern hemispheres. In the Northern Hemisphere, south is the direction toward higher sun angles and increased solar radiation, whereas in the Southern Hemisphere north is that is the direction toward higher sun angles and increased solar radiation. The key difference is the direction toward the Equator, which is south in the northern half the world and north in the southern half.

*It does not, however, work at the poles, where the sun angle does not change over the course of a day.

At first glance, latitude and longitude seem like equivalent concepts. On any local-scale map, lines of latitude (parallels) and longitude (meridians) form a grid, with the two sets of lines intersecting at 90° angles. On such maps, lines of longitude as well as those of latitude appear to be parallel to each other. Many world maps, such as those using a Mercator projection, have the same appearance, with latitude and longitude forming a grid of rectangles.

Such maps, however, are misleading, as longitude is very different from latitude. And as can be seen on a globe, they do not actually form a grid with the two sets of lines intersecting at 90° angles.  Only lines of latitude are parallel to each other and are always the same distance apart, approximately 69 miles per degree. Lines of longitude are also approximately 69 miles per degree – but only at the Equator. The farther they are from the Equator, the closer they are to each other. In Bozeman, Montana, which is about halfway between the Equator and the North Pole, a degree of longitude covers about 49 miles, and at latitude 85° the figure is only six miles. At the poles, all lines of longitude converge at a single point.

Lines of latitude and longitude also differ in length. All meridians (lines of longitude) are of the same length. Running from the South Pole to the North Pole, they go halfway around the Earth, approximately 12,430 miles. The Equator, latitude 0°, goes all the way around the Earth and is approximately 24,901 miles long. But the farther they are from the Equator, the shorter the parallels (lines of latitude) become. The 45° latitude line, which is just a little south of Bozeman, is approximately 17,617 miles long, whereas the 85° latitude line is only 434 miles long. At 90°, the north and south poles, latitude does not form a line at all but is instead reduced to a single point.

Perhaps the most important biggest difference between these two groups of imaginary lines is the fact that latitude designations are set by nature whereas longitude designations are essentially arbitrary creations of the human mind. The Equator and the poles are defined by the spin of the Earth’s around its axis and therefore have fixed locations. All other lines of latitude are defined in relation to the Equator and the poles and therefore could only be located exactly where they appear on maps and globes. But longitude is different. The Prime Meridian, 0° longitude, could be any line that runs from the North Pole to the South Pole. In earlier times, different lines of longitude were defined as 0°. Consider for example, the well-known world map of Abraham Ortelius, made around 1570. On this map, the Prime Meridian runs through the Atlantic Ocean, whereas today it runs through western Europe and western Africa. Ortelius also measured longitude from 0° to 360°, going all the way around the Earth, which makes perfect sense. Today we measure longitude from 0° to 180° to the west and to the east of the Prime Meridian, which is equally reasonable. In contrast, measuring latitude in any way other than from 0° to 90° makes no sense at all.

To see how lines of longitude are measured as angles we can once again imagine a slicing a globe in half, only this time through the equator. Again, circles are formed on the flat sides of the two resulting hemispheres. A line drawn from the center of one of these circles to any point on its edge could be used to define the Prime Meridian, a line running from that point on the surface of the Earth to both poles. Other lines going from the center to the edge of the circle form angles with the Prime Meridian, which are used to define the other meridians. The diagram posted below shows a series of 10° angles, which in turn define a series of longitude lines separated from each other by 10° (which range, on this diagram, from 40° east to 110° west of the Prime Meridian.)

On the opposite side of the Earth from the Prime Meridian is the 180° degree line of longitude. As it is equally far to the west as it is to the east of 0° longitude, it does not have an “E” or “W” designation. On many world maps, this line of longitude appears twice, on both the left side and the right side of the image. The 180° degree line of longitude also forms the foundation of the International Date Line, as we will see in a later post.

Because longitude is quite different from latitude, the east/west direction is quite different from the north/south direction, as we will see in the next post.

Latitude, as we have seen, is closely connected to midday sun angles. Because of this relationship, latitude has long been relatively simply to measure. Four hundred years ago, navigators could easily determine how far they were to the north or south of the Equator if the day was clear and they had kept track of the date. All they had to do was measure the angle of the sun at its highest position and consult a table that gave the latitude at which the sun reached the zenith on that day. If, for example, they measured the noon sun angle at 60° on March 20, when the sun is directly overhead at the Equator (0°), their own latitude had to be 30°.

On a clear night in the Northern Hemisphere [1], navigators could also measure the angle of the North Star, also called Polaris, which is always almost directly above the North Pole. The farther they had sailed to the north, the higher in the sky the North Star would be. In fact, the angle of Polaris is equal to the latitude of the observer. If Polaris is measured at 70° above the horizon, then the place at which the measurement is made must be 70° N latitude. At the North Pole, 90°N latitude, North Star is almost exactly overhead, or 90° above the horizon.

Sailors were not the only people to rely on the North Star for navigation. In the United States before the Civil War, escaped slaves heading for freedom usually traveled at night without a compass or map. To keep traveling northward, they typically used Polaris as a guide.

Because latitude has long been measurable, most world maps made in the 1500s and 1600s have a relatively high degree of accuracy in the north-south direction. Those same maps, however, are often strikingly inaccurate in the east-west direction. In those days, a ship’s longitude, or position in the east/west direction, could not be measured. Inaccurate maps resulted in countless shipwrecks, creating a huge problem that demanded a solution. As we will see in a later post, the solution to the longitude problem was to develop sturdy clocks that would remain accurate on storm-tossed ships. If latitude is essentially about sun angles, longitude is essentially about time.

The paired maps posted illustrate the higher degree of accuracy of early maps in the north/south direction (latitude) than in the east/west direction (longitude). If you trace out the Equator and the tropics of Cancer and Capricorn on the Ortelius map, made around 1570, and the compare them with the same lines on the modern map, you will see that they generally pass through the same places. On both maps, for example, the Tropic of Cancer just clips the Mexican peninsula of Baja California and passes just to the north of Cuba. Similarly, the Equator cuts just to the south of the Malay Peninsula on both maps. In contrast, many longitudinal positions vary greatly on the two maps. South America, for example, is shown as extending across many more degrees of longitude in the Ortelius map than it actually does.

[1]. There is a similarly positioned “South Star,” Sigma Octantis, that could conceivably be used for the same purpose in the Southern Hemisphere. It, however, “is too dim to be a convenient celestial reference point for stargazers and navigators.”