Chapter 3

Grid and Bear It

In This Chapter

bulletGetting it right with a grid

bulletPointing someone in the right direction

bulletDiscovering a common theme: Degrees, minutes, and seconds

bulletLocating a street address and global address

W elcome to Gridville, the cute little burg shown in Figure 3-1. You and I are going to pay this town a quick visit because it looks like a great locale to review basic concepts of location, plus latitude and longitude, the topics of this chapter. I say “review” because if you are like most people, then you probably learned about these things during elementary or junior-high school, but may have forgotten some or most of it later on.

Knowledge of latitude and longitude gives you basic location and orientation skills regarding our planet Earth. It also affords the opportunity to learn all sorts of little tidbits, which, in addition to impressing your friends, can greatly enhance your understanding of geography.

Feeling Kind of Square

To get started, look at Figure 3-1 and familiarize yourself with Gridville. In particular, note the following:

bulletThe roads are aligned with the cardinal directions — that is, they run north-south or east-west. The result is a grid pattern of north-south roads that intersect east-west roads at right angles. So getting right with Gridville means getting used to a city that is all right angles and nothing but right angles. Thus, I’ll understand if this town leaves you feeling a little square.


bulletNorth is toward the top of the map; south is toward the bottom; east is toward the right; and west is toward the left. This is a near-universal rule in map-making, but you should always carefully examine the map you are looking at and confirm which way is which.

bulletGridville has a principal east-west road named Equator Boulevard, and a principal north-south road named Prime Meridian Way. The two roads cross in the middle of Gridville.

bulletEvery other road in Gridville has a name that refers to its location relative to those two roads. Thus, streets are numbered consecutively north and south of Equator Boulevard. Avenues are numbered consecutively east and west of Prime Meridian Way.

bulletA big dot and a letter mark two intersections. I’ll refer to these shortly.

Telling Someone Where to Go

Because geography involves locations and directions, it affords ample opportunity to tell someone where to go. Suppose you live in Gridville and are standing on the sidewalk at Point A, the corner of North 4th Street and East 3rd Avenue. A stranger from out of town comes up to you and asks for directions to Gridville Hospital — can you help her?

Of course you can. You know the hospital is located at Point B on the map. And you can convey that information to the stranger by stating either the hospital’s relative location or absolute location.

Relative location

In the first instance, you can tell the stranger how to get to the hospital from Point A. For example (pointing west along North 4th Street), “Go that way four blocks, turn left, and walk five more blocks.” This is called relative location because the information you gave is relative to Point A. Give those directions verbatim to the stranger at any other intersection in Gridville, and the result is a lost stranger.

Absolute location

As an alternative, you can convey the location of the hospital with respect to its grid coordinates — that is, its location within the grid system. For example, “Go to the corner of South 1st Street and West 1st Avenue.” This is called absolute location because theoretically, those directions work anywhere in Gridville, not just at Point A.

The best location to use

Both relative location and absolute location have the potential of getting the stranger to the desired destination. And chances are you have used both types of location to direct someone to a destination in your town, neigh- borhood, or environs.


But in a global context, absolute location is far superior to relative location. When you think about it, the task of directing somebody to a location half-way around the world by means of relative location (e.g. “Go that way 11,238 miles and turn right”) is rather mind-boggling. And even if you could do it, that information would only work at the one location where that information was given. It would be far better if every place on Earth had an absolute location such as that hospital in Gridville. Of course, that would be contingent on the existence of a global grid that basically mimics what we’ve seen in Gridville. Fortunately, such a grid exists.

The Global Grid: Hip, Hip, Hipparchus!

Like Gridville, the world as a whole possesses a grid whose coordinates may be used to identify the absolute location of things. Indeed, that is why a Greek named Hipparchus invented the global grid some 2,200 years ago.

As chief librarian at the great library in Alexandria, Egypt, Hipparchus compiled information about lands and cities all over the expanding Greek world. He saw the value of accurately locating objects on a map, but in those days that was easier said than done. Maps were notoriously inaccurate, due in good measure to lack of a systematic means of stating the location of things. So Hipparchus set out to rectify the situation, and came up with the global grid that is still in use today (see Figure 3-2).

Avoiding gridlock


Proper use of a grid coordinate system to state the absolute locations of things depends on a handful of prerequisites. Think of these as ways of avoiding gridlock:

bulletFamiliarity breeds success. Knowledge of the naming and numbering of grid components is essential. If, for example, that stranger were not familiar with Gridville’s grid, then telling her the hospital is at “the intersection of South 1st Street and West 1st Avenue” would have made no sense whatsoever. The same is true with respect to the global grid. That is, knowing how the lines are named and numbered is essential if you are to use the grid successfully.

bulletUnique components. Each road in Gridville and each line on the global grid must have a unique name. In Gridville, for example, there must be only one road named South 1st Street, and only one named East 1st Avenue. If multiples exist, then more than one site could satisfy “the intersection of South 1st Street and East 1st Avenue.” And that would rather defeat the concept of absolute location, whether in Gridville or around the globe.

bulletNo double-crossing allowed. Don’t take that as a threat or accusation. What I mean is two roads in Gridville may cross each other only once. The same goes for two lines on the global grid. If they have multiple junctions then, such as the last point, there would be two or more intersections of, say, South 1st Street and East 1st Avenue. And again, that would defeat the concept of absolute location.

bulletFull names, please. You must use the full name of each road in Gridville and each line on the global grid. Again, the absolute location of the hospital is the intersection of South 1st Street and West 1st Avenue. Now suppose you had told that stranger, “The hospital’s at the corner of 1st Street and 1st Avenue.” Well, if you look carefully at the map of Gridville, you find four locations where a 1st Street crosses a 1st Avenue. Obviously, the potential for location confusion here defeats the purpose of absolute location. The remedy is to use the full name of each grid component.

The naming game


While the Gridville grid consists of real roads, the global grid consists of imaginary lines of latitude and longitude (see Figure 3-2). Latitude lines go across the map — latitude comes from the Latin latitudo, meaning breadth, or the measure of the side-to-side dimension of a solid. Longitudelines run from top to bottom — longitude comes from the Latin longitudo, meaning length. This makes sense because when viewed on a globe, lines of longitude are generally lengthier than lines of latitude.

Similar to the roads in Gridville, the global grid contains a principal line of latitude (the equator) and a principal line of longitude (the prime meridian). All other lines of latitude and longitude are named and numbered respectively from these starting lines. It makes sense, therefore, that if you want to make like Hipparchus and draw a grid on a globe, then these are the first two lines you would draw. But where would you put them, and why?

The equator

Because Earth is sphere-like, no compelling locale cries out and says, “Use me to locate the equator!” So where to put it? Old Hipparchus might simply have said, “It’s Greek to me!” and placed it anywhere. Instead, he wrestled with the challenge and came up with an ingenious solution.

He knew that the Earth is sphere-like and that it rotates around an imaginary line called the axis. Look on a globe and you find two fixed points, halfway around the earth from each other, where the axis intersects the Earth’s surface: the North Pole and the South Pole. So Hipparchus drew a line that ran all the way around the globe and was always an equal distance (hence, equator) from the two Poles. The result is a latitudinal “starting line” from which all others could be placed on the globe.

The prime meridian

The longitudinal “starting line” is called the prime meridian, which signifies its importance as the line from which all other lines of longitude are numbered. Locating this line proved more problematical than locating the equator. Quite simply, no logical equivalent of the equator exists with respect to longitude. Thus, while the equator came into general use as the latitudinal starting line, mapmakers were perfectly free to draw the longitudinal starting line anywhere they pleased. And that is what they did.

Typically, mapmakers drew the prime meridian right through their country’s capital city. By the late 1800s, lack of a universal prime meridian had become a real pain in the compass. International trade and commerce were growing. Countries were claiming territory that would become colonial empires. But one country’s world maps did not agree with another’s, and the international climate made it increasingly advisable that they do so.

As a result, in 1884 the International Meridian Conference was convened in Washington, D.C. to promote the adoption of a common prime meridian. Out of that was born an agreement to adopt the British system of longitude as the world standard. Thus, the global grid’s prime meridian passes right through the Royal Greenwich Observatory, which is in the London suburb of Greenwich, as well as parts of Europe, Africa, and the Atlantic Ocean. The British system was chosen largely because in 1884 Britain was the world’s major military and economic power, and also had a fine tradition of mapmaking.

Getting Lined Up

With the starting lines in place, one can now contemplate putting all of the other lines of latitude and longitude on a globe. In doing that, Hipparchus used the notion that 360 degrees (°) are in a circle. Accordingly, he drew lines of latitude such that each and every one is separated by one degree of arc from the next. He then did the same with longitude. This is why lines of latitude and longitude are referred to as degrees.

Why is Earth 360° round?

The ancient Sumerians believed there were 360 days in a year. Like other civilizations way back when, the Sumerians equated their gods with celestial objects. Not surprisingly, the sun god was especially important. Because it took the Earth 360 days to travel around the sun (or so they believed), the Sumerians figured the number 360 had extra-special significance. As a result, they developed a system of mathematics based on multiples of 6 and 60. Nowadays, we would call it base-6 mathematics or (get ready for this) a sexagesimal system. In any event, 6 × 60 = 360.

The ancient Egyptians adopted the ancient Sumerians’ numerical ideas, and eventually discovered the error concerning the length of the year. But by then, however, the number 360 had achieved such acceptance and status that the Egyptians decided not to mess with it. Accordingly, they kept the 360-day year but, being fun-loving people, added an annual 5-day holiday.

The ancient Greeks, like the ancient Egyptians, were adept at adopting things and ideas from civilizations more ancient than they. So when Hipparchus, in about 140 B.C., began fiddling with the notion of dividing a circle (and Earth) into degrees, he chose the number 360.

What’s wrong with this map?

The answer to the headline is this: Nothing much, really. You could say the map is upside down, and you would be right to a point. After all, nowadays maps commonly have north at the top. But considered as a planet in the multi-dimensional vastness of space, Earth has no “right side up.” Thus, no compelling scientific reason exists as to why you can’t make a map with south toward the top — other than that it would look strange and confusing to most people. Indeed, in olden times maps were oriented every which way. It was only with growing availability and use of the magnetic compass in the early Middle Ages that it became common to make maps with north toward the top, just as the compass pointed. Hoping to end confusion regarding direction, in 800 A.D., Charlemagne decreed that thenceforth all French maps would be made with north at the top, that direction to be indicated by the fleur-de-lis. Other lands quickly followed suit. Thus, the emperor’s edict became and remains the global standard.



The system of latitude lines has the following characteristics:

bulletLines of latitude run across the map (east-west) and are called parallels because each line of latitude is parallel to every other line of latitude.

bulletThe equator (Latitude 0°) divides the world into the Northern Hemisphere and the Southern Hemisphere.

bulletStarting from the equator, each successive line (degree) of latitude is numbered consecutively both to the north and to the south as far as the North Pole (Latitude 90° North) and South Pole (Latitude 90° South).

bulletExcept for the equator, each line of latitude is identified by a number between 0 and 90 and by the word North or South (or the abbreviations N or S) to indicate its location north or south of the equator. Thus, the line that is 20 degrees north of the equator is referred to as Latitude 20° North. It would be misleading and incomplete to just call this line “Latitude 20” because another line of latitude south of the equator could also be called “Latitude 20.”

bulletOnly one line of latitude is a great circle, a line that divides the Earth in half.



The system of longitude lines has the following characteristics:

bulletLines of longitude run from the North Pole to the South Pole (top to bottom of the map) and are called meridians.

bulletAs opposed to latitude, no two lines of longitude are parallel to each other. Rather, successive lines of longitude are about 70 miles apart at the equator, but from there they slowly converge until they come together at the two poles (see Figure 3-2).

bulletThe prime meridian (Longitude 0°) divides the world into the Eastern Hemisphere and the Western Hemisphere.

bulletStarting from the prime meridian, every line (degree) of longitude is numbered consecutively to the east and to the west half way around the world. Because Earth is 360 degrees around, 180 degrees of longitude lie east and west of the prime meridian.

bulletEvery line of longitude (except the prime meridian and the 180 degree line) is identified by a number from 1 to 179, and by the words East or West (or the letters E or W) to indicate its location east or west of the prime meridian. Thus, the line that is 20 degrees east of the prime meridian is referred to as Longitude 20° East. It would be misleading to call this line “Longitude 20” because some another line that is 20 degrees west of the prime meridian also could be called “Longitude 20.”

bulletEvery line of longitude, is a great circle — a line which, if continued around the world, would divide the Earth equally in half.



As far as geographers are concerned, latitude and longitude make for a very special grid that deserves a special name, the graticule, to distinguish it from every other kind of grid. Indeed, this name is so special that many dictionaries and computer spell-check programs do not recognize it. But geographers do, and they are extremely impressed if they hear it used by a layperson.

But more important than saying “graticule” is the ability to use it properly. That means, among other things, correctly identifying the grid coordinates (latitude and longitude) of locations indicated on a map. With that in mind, take a look at Figure 3-3, which represents a portion of the graticule. Note that lines of longitude are shown parallel (when in reality they converge toward the poles) and that only every tenth degree line of latitude and longitude are indicated. World maps typically “skip” lines in a similar fashion, lest they become cluttered by the graticule. But what I really want you to focus on are the three dots lettered A, B, and C. See if you correctly can identify the coordinates of each dot, keeping in mind the following rules:

1 .When reporting coordinate locations, always give the latitude first, and then give the longitude. (Why? I have no idea, and I don’t think anybody else does either. It’s just the rule.)

2. Correct reference to latitude must specify whether a location is north or south of the equator (Latitude 0°), assuming the location is not on the equator itself.

3. Correct reference to longitude must specify whether a location is east or west of the Prime Meridian (Longitude 0°).

The correct locations of the dots are as follows:

A = Latitude 20° North, Longitude 10° West

B = Latitude 5° South, Longitude 20° East

C = Latitude 22° South, Longitude 17° West


Q. Why did the chicken cross the equator? A. To get to the other hemisphere.

Q. Why was longitude boiling mad? A. Because it had 360 degrees.

Q. Why weren’t there any parallels on the map? A. Because the cartographer had no latitude in the map’s design.

Q. Why were the meridians lost? A. Because they were in a parallel universe.

Had enough? I certainly have. But if this is your idea of humor, you can get more of it on the geography page (

Minutes and seconds that don’t tick away

On Earth’s surface, adjacent lines of latitude and longitude may be several miles apart, and that creates a potential problem if you wish to state the absolute location of a spot that is “between the lines.” For this reason, the graticule contains a couple of levels of refinement (see Figure 3-4).

First, the space between successive degree lines may be subdivided into 60 equidistant units called minutes (‘). Second, the space between successive minute lines may be subdivided into 60 equidistant units called seconds (“). And if more exactitude is needed, then seconds may be carried out to as many decimal points as may be necessary. I’ll show you an example in just a second, but that reminds me to make a point.

Doesn’t this sound familiar? Sixty seconds in a minute? And for good reason. The system that you use to tell time goes back to the same Sumerian base-6 arithmetic that Hipparchus used to divide up a circle and also the world. Hmmm . . . there are 24 hours in a day. Think 24 being evenly divisible by 6 is just a coincidence? No way.


Applied Geography: Using GPS to save Asia’s tigers

Press a button on a GPS and it gives your precise latitude and longitude. What’s a GPS? It stands for Global Positioning System and involves a hand-held device about the size of the remote control for your TV. Courtesy of the U.S. Defense Department, a number of satellites orbit Earth and constantly calculate their precise locations. When you activate a GPS, it acquires location data from 3 or 4 of those satellites and uses it to calculate its own location in degrees, minutes, and seconds of latitude and longitude. It’s an amazing piece of technology that has all kinds of applications. Take saving the tiger, for instance.

Asian tigers are highly endangered in the wild because human activities (mainly farming and forestry) have reduced their natural habitat. Governments in affected areas are striving to create natural tiger preserves, but a major problem is that nobody knows exactly how much habitat a tiger needs to behave like a normal tiger. Recently, researchers were able to stun a wild tiger and attach to it a collar that contains a GPS and data recorder. Every so often the device activates, calculates the tiger’s location, and records it. After a couple of weeks, the collar detaches and sends a signal that enables the researchers to find it. What they collect, of course, are data that allows them to map the animal’s wanderings and therefore get a good idea of exactly how much land a tiger needs.

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