This discovery prompted me to begin mapping the locations of the world’s top companies and how these geographical patterns changed over time. My initial efforts will be focused on market capitalization, which limits me to publicly traded companies. If privately held companies could be considered in an assessment the world’s top companies by valuation, the results would probably be similar but not the same. Difficulties in estimating the value of private companies, however, preclude this option [1].

The map posted below shows the locations of the headquarters of companies with current (December 2025) market capitalization of over one trillion U.S. dollars. Nine of these eleven firms are American. More surprising, all nine have headquarters west of the Mississippi River. The west coast, particularly the San Francisco Bay Area, dominates the map. This preponderance would have been more pronounced if Tesla had not moved from Palo Alto, California to Austin, Texas in 2021. (Note that these circles are not precisely placed; if two or more firms are located in the same city or even the same metro area, their corresponding circles are simply offset from each other so that they are all visible. Forthcoming posts will examine smaller areas to allow more precisely mapping.)

The next issue is whether similar geographical patterns hold for companies in the next tier down, those with market capitalization between $500 billion and $999 billion. As the next map shows, only seven companies fall in this category. All but one are located in the United States. Of these six firms, four are headquartered west of the Mississippi River. Only one, however, is in the San Franciso Bay Area, whereas two are in Texas. But until 2020, Oracle’s corporate headquarters had been on the shore of San Francisco Bay; it is now in Austin, Texas.

The final map combines the spatial information found in the first two and adds two additional circles to cover the full top-twenty list (found in the first illustration). These circles represent Samsung, headquartered in Seoul, South Korean, and Johnson & Johnson, headquartered in New Brunswick, New Jersey, on the outskirts of the New York City. What strikes me most about this map is the absence of circles in Europe and Japan. To what extent does this pattern hold as we move down the list of the top companies by market capitalization? That will be the topic of the next GeoCurrents post.

[1] ChatGPT tells me that OpenAI would rank in 18^th place, at $500 billion estimated private valuation, with SpaceX ($400 billion) not far behind – although the same chatbot also states that “recent discussions [of SpaceX] point toward ~ $800 billion in a share sale/secondary sale,” which would put it in 15^th place. Grok agrees with the $500 billion figure for OpenAI and the $400 billion figure for SpaceX, but claims an estimated valuation of $480 billion for China’s ByteDance, which ChatGPT pegs at $220 billion, indicating both the depth of the problem and the limits using AI for such information.

A more severe difficulty arises with secretive private companies that are enormous in terms of revenue, but whose valuation remains highly uncertain. According to ChatGPT, the top firms in this category are Vitol, based in Switzerland and the Netherlands, and Singapore-based Trafigura.

(Note: Shortly after this post went up, I read that SpaceX is planning an initial public offering in 2026, “with a report suggesting the company would target a $1.5 trillion valuation.” SpaceX is headquartered in far southern Texas, in the town of Starbase, formerly Boca Chica Village, with an estimated population of 500.

The post Almost All of the World’s Top Companies by Market Valuation Are Based in the United States appeared first on GeoCurrents.

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.”

The post My Map of Climes: Latitudinal Zones Defined by Earth/Sun Relations appeared first on GeoCurrents.

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.

The post More Cartographic Misinformation on Global Climate Zones appeared first on GeoCurrents.

The main reason why the common conception of the subtropics does not match the formal definition is because the former is based on climate and climatic zones do not rigidly follow latitudinal belts. As can be seen below, the Wikipedia map of subtropical climates strays far from the lines of latitude that supposedly bound them. Although the Wikipedia article on the subtropics does not specify that the latitude-based definition of the term is quite different from the climatological definition, both ChatGPT and Grok do so.  As a result, they give a better sense of what the term actually means.

But even if we limit ourselves to the climatological subtropics, conceptual problems remain. To begin with, the definition of the term varies significantly from source to source. Such definitions, moreover, are often too vague to be useful. ChatGPT, for example, tells me that “Some meteorological sources define the subtropics as the region where [the] mean annual temperature is above 18°C (64°F) [and] winters are not cold enough for snow to be reliable,” but as this definition also includes the tropics. ChatGPT further claims that subtropical summers are hot, but that is not the case in many west-coast locations. In Walvis Bay, Namibia, which at 22°57’ is just north of the Tropic of Capricorn, not a single month has a mean daily maximum temperature above 68.5° F (20.3° C). Grok’s climatological definition of the subtropics, in contrast, is precise and seemingly scientific: “Regions where the average temperature of the coldest month is between 0–18 °C (32–64 °F) and the average temperature of the warmest month is above 22 °C (72 °F), following modified Köppen climate classification criteria.” But the “0–18 °C (32–64 °F)” coldest-month range is how the Köppen system defines temperate climates, not subtropical ones.

The Wikipedia article on the subtropics rests on more solid climatological grounds. It follows the Trewartha climate classification system in defining a subtropical climate as one “that has at least eight months with a mean temperature greater than 10 °C (50.0 °F) and at least one month with a mean temperature under 18 °C (64.4 °F).” The main problem with this definition is that it fails to exclude areas with short but chilly winters that have regular bouts of extreme cold – conditions that few people would regard as “subtropical.” Chattanooga, Tennessee, for example, easily slots into Trewartha’s humid subtropical zone, but its mean monthly minimum temperature in January is a frosty 15.9° F (-9.5° C) and its record low is a frigid -10° F (-23° C).

Another way to define the subtropics is by the geographical ranges of certain perennial plants, generally those that require a long period of relatively warm weather but can tolerate cool winters with occasional light frost. The Wikipedia article, for example, tells us that “These [subtropical] climates do not routinely see hard freezes or snow due to winter on average being above freezing, which allows plants such as palms and citrus to flourish.” By this criterion, my own home on the Stanford campus near Palo Alto, California (37° N), is definitely subtropical. But I doubt that anyone who grew up in the area would regard it as such. Most local people whom I queried seemed puzzled that I would even ask such a silly question. Several of them replied that Hawaii is the quintessential subtropical location. Actually, Hawaii is fully tropical (the northernmost point on Kauai is at 22°13′ N latitude).

My own personal definition of the subtropics is keyed to a more comprehensive botanical list found in the same Wikipedia article: “plants such as palms, citrus, mango, pistachio, leechee, and avocado are grown in the subtropics.” Avocado trees cannot be successfully cultivated in Palo Alto, as they succumb to periodic frosts (Palo Alto’s mean annual minimum temperature is 28.1° F [-2.2° C]). When driving south, I can only start to imagine that I have entered the subtropics when I have rounded Point Conception and see the avocado orchards of southern California. Santa Barbara’s mean annual minimum temperature is 36.6° F (2.3° C) and frost-sensitive plants abound. But good luck with mangos and leechees.*

I do think that the “subtropics” is an indispensable geographical category. But it is necessary to clearly distinguish the “latitudinal subtropics” from the “climatological subtropics.” I also think that it is essential to consider regularly occurring extremely low temperatures when defining the subtropics on climatic grounds. These topics will be considered in greater length in coming GeoCurrents posts.

* As the map posted below shows, avocado orchards are found north of Point Conception in San Luis Obispo County, but I have never seen them.

**ChatGPT tells me that “You can grow mango trees in Santa Barbara if you have a warm microclimate and are willing to protect the tree during cold spells. They are not guaranteed producers…” It essentially gives the same answer for leechees.

The post The Incoherent Concept of the Subtropics appeared first on GeoCurrents.

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.

The post Avoiding Misinformation When Teaching the Geography of Climate; Part 2, Climate Maps appeared first on GeoCurrents.

The actual situation, however, is far more complicated. Climate is not just a matter of average temperatures, nor are average temperatures just a matter of latitude. Even equatorial locations can have cool climates if they sit at high elevations; Quito, Ecuador, at 0° latitude and an altitude of 9,350 ft (2,850 m), has a mild annual daily mean temperature of 60.1° F (15.6° C). And even tropical lowland areas can have seemingly non-tropical climates. Consider, for example, the coastal city of Lima, Peru, which, at 12° S, is well within the tropics. Yet in December, a month with high sun angles, Lima’s mean daily maximum temperature is only 74.9° F (24.4° C), and in August it is only 66.6° F (19.2° C). Unlike most tropical locations, moreover, Lima receives very little rainfall and has nothing that even approaches a rainy season. In August, the city’s “wettest” month, average precipitation is a meager 0.06 inches (1.5 mm). But despite its extreme aridity, with only 0.25 inches (6.4 mm) of rain annually, Lima remains humid throughout the year. In its driest months (December-January), the average relative humidity is 81%.

Lima owes its mild temperatures, lack of precipitation, and humid air to the cold Humboldt Current that courses off its coast. Besides latitude, altitude and proximity to ocean currents are thus key influences on the geography of climate. But they are still not the only ones. Other important considerations include location relative to mountain ranges and prevailing winds, and position within continental landmasses (coastal vs. interior and west coast vs. east coast). These factors will be explored in later posts. For now, I will remain focused on the understandable but simplistic notion that latitude alone determines climate.

Equating climate with latitude with goes back to the ancient Greeks, whose geographical knowledge was largely restricted to the greater Mediterranean world. The term “climate” derives from the Greek term klima, which originally meant “inclination” or “slope.” Greek geographers divided the world into distinct bands called “the climes,” which were strictly defined by latitude, which in turn was defined by the seasonally changing inclination of the sun. In their simpler five-clime model*, used by Aristotle and others, a hot “torrid zone” extended from the Tropic of Cancer to the Tropic of Capricorn. On either side of this tropical (or equatorial) swath lay two temperate belts, which extended to the Arctic and Antarctic circles. Beyond the circles were the frigid, or arctic and Antarctic, zones. Most ancient Greek geographers agreed that only the temperate zone was inhabitable, as the torrid zone was too hot for human habitation and the arctic zone too cold. The existence of the vast torrid zone meant that the ecumene (or oikoumene), the inhabited temperate portion of the world, was isolated from any possible human societies living in the southern temperate belt.

Ancient Greek climatic ideas were highly influential in ancient and medieval Europe, discouraging ventures into far northern and far southern lands. Eventually, however, the weight of empirical evidence crushed the authority of the classical texts. As Margaret Small explains in her 2020 book Framing the World: Classical Influence on Sixteenth-Century Geographical Thought:

[This] chapter first examines how and why the Greeks and Romans developed the concept of uninhabitable frigid and torrid regions denoting the limits of the oikoumene [ecumene]. In the process it demonstrates why these climatic limits became conceptual margins that hindered exploration for nearly two thousand years. It looks at the reevaluation of authority which still saw the Greeks and Romans as the arbiters of knowledge, but enabled non-canonical classical authors to become important in revising attitudes to the climatic zones which had once been thought to define the edges of the oikoumene. In the new geography, the arctic and equatorial regions were believed to play key roles in allowing the different parts of the world to interact with one another. Without this shift in mind-set about the frigid and torrid zones, it would have been impossible for Europeans to begin to think of the world as a single, exploitable, global unit, created by God for human dominion.

The actual contours of global climate were gradually revealed during and after the sixteenth century, and the process was nearly completed with the pioneering research of geographer Alexander von Humboldt (1769-1869). Unfortunately, however, the original latitude-focused model never disappeared in pedagogical circles. In preparing this post, I was surprised to find many educational climate maps that are not merely outdated but are filled with misinformation. Several of these maps will be examined in the next post.

*  Ptolemy used additional lines of latitude to delineate seven climes, based on periods of daylight on the summer solstice. This scheme gained considerable importance in medieval Europe and in the Islamic realm.

The post Avoiding Misinformation When Teaching the Geography of Climate, Part 1 appeared first on GeoCurrents.

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

The post Time Zones Are Based on Longitude Overruled by Political Geography appeared first on GeoCurrents.

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.”

The post If Latitude Is about Sun Angles, Longitude Is about Time appeared first on GeoCurrents.

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.

The post The Misperceived Directional Orientation of the East Coast of North America appeared first on GeoCurrents.

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.

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