How to Read a Map

nansenmap.gif (21869 bytes)

Have you ever stopped to consider that the North Pole is not the top of our Earth?

No way, you say?

Yes way. In our very Euro-North American-centric way of thinking, we've always called the North Pole the "top" and the South Pole the "bottom" because that's the way every globe that I've ever seen depicts the Earth. But those globes could just have easily and just as accurately been depicted with Antarctica on "top."

In the grand scheme of the Universe, there is no "up" or "down" so to speak. These terms are useful on a planet like ours where gravity tugs at our feet, but seen from outer space, the Earth could just as easily be viewed with Antarctica on top, or sideways, for that matter.

Top as north and bottom as south are conventions, artifacts, decisions made a long time ago that have been part of our culture for so long that we don't even question them. But as the world's peoples start talking more, the people living "down under" are beginning to take exception to those decisions.

A former student of mine, screenwriting partner and good friend, Frank M, made me aware that in Costa Rica, they say that "us" (people living in North America) are the ones who are down under: up there means headed towards Antarctica, down the coast means headed towards the United States. He even went so far as to say that some people "resent" the fact that we assume that we're on top and they're on bottom. (Trying to work out the PC thing to say might be difficult in this case, however. Maybe we should all just slide, slippery slide to Will Smith songs, forget about top and bottom.)

Even though it may sound bass ackwards, the honest to gosh truth is that Antarctica could be the top. The only thing that "prevents" it from being the top is convention and history.

Which brings us to our topic for this particular lecture: maps and navigation. Let's define these words first.

The WWWebster Dictionary again...

Main Entry: 1map
Pronunciation: 'map
Function: noun
Etymology: Medieval Latin mappa, from Latin, napkin, towel
Date: 1527
1 a : a representation usually on a flat surface of the whole or a part of an area b : a representation of the celestial sphere or a part of it
2 : something that represents with a clarity suggestive of a map
3 : the arrangement of genes on a chromosome -- called also genetic map
- map·like /-"lIk/ adjective
- on the map : in a position of prominence or fame <had put the fledgling university on the map -- Lon Tinkle>


Main Entry: nav·i·ga·tion
Pronunciation: "na-v&-'gA-sh&n
Function: noun
Date: 1547
1 : the act or practice of navigating
2 : the science of getting ships, aircraft, or spacecraft from place to place; especially : the method of determining position, course, and distance traveled
3 : ship traffic or commerce
- nav·i·ga·tion·al /-shn&l, -sh&-n&l/ adjective
- nav·i·ga·tion·al·ly adverb

Maps are representations of the surface of our planet, oftentimes, including the undersea surface, i.e. the sea bottom. They can be two- or three-dimensional on a flat surface (we'll talk 3-D representations, or contour plots, later) or they can be three-dimensional on a spherical surface, such as a globe. (Someone might object to me calling a globe a map but, in my opinion, a globe is a representation of our celestial sphere in the same way that a map is.).

Navigation is a science (some would call it an art!) that gets us from point A to point B, essentially. They mention ships, aircraft and spacecraft (how many of you have navigated a spacecreaft?!) but they left out cars, motorcyles, mopeds, bicycles, skis, dog sleds and any of the other myriad forms of transportation that takes us from one place to the next.

All the same, it follows logically that if you want to go somewhere, you will probably need a map; hence, my coverage of these two topics in the same lecture.

We'll start with some general features of maps, but let me say first that we're only going to cover the essential features of maps that allow us to "navigate" across the oceans, identify locations and calculate distances from one point to the next. Map reading is extremely important to oceanography, whether used for navigating a ship or for representing properties of the ocean, such as sea surface temperature or ocean color. But we're not going to cover all the different ways in which a spherical globe can be projected on a flat surface. Suffice it to say that different projections serve different purposes and are useful to different people in different ways. For our purposes, we'll stick with one type of map projection, the Mercator Projection. For more info on map projections, visit Peter Dana's Introduction to Map Projections, (, courtesy of The Geographers Craft, Virtual Geography Department, University of Texas at Austin.

Just to give you a flavor of what I mean and to introduce you to the Mercator projection (the one with which we are probably the most familiar), here's a map showing three projections of the United States. (I stole this map from Peter Dana. It makes me feel like a sea pirate to steal a map, a bit of the ol' salt coming out. Peter, if you want it back, I'm happy to return it.)

threeprojections.gif (9535 bytes)

Take a few moments to study this map. What are the differences between the three projections? Which one looks "right" (trick question)? Again, if you are interested in knowing more about how maps are made, take a look at Peter's web site.

In this course, the two most important features you need to be able to identify on a map are the latitude and the longitude. (Oh boy, here we go...) Pay careful attention to these descriptions. It's not difficult but students get confused mostly because they don't pay close attention. After the description, I'll provide a couple maps and map references so you can practice your new-found knowledge.

Cross circuit to my handy-dandy web dictionary...

Main Entry: lat·i·tude
Pronunciation: 'la-t&-"tüd, -"tyüd
Function: noun
Etymology: Middle English, from Latin latitudin-, latitudo, from latus wide; akin to Old Church Slavonic postilati to spread
Date: 14th century
1 archaic : extent or distance from side to side : WIDTH
2 : angular distance from some specified circle or plane of reference: as a : angular distance north or south from the earth's equator measured through 90 degrees b : angular distance of a celestial body from the ecliptic c : a region or locality as marked by its latitude
3 a archaic : SCOPE, RANGE b : the range of exposures within which a film or plate will produce a negative or positive of satisfactory quality
4 : freedom of action or choice
- lat·i·tu·di·nal /"la-t&-'tüd-n&l, -'tyüd-; -'tü-d&n-&l, -'tyü-/ adjective
- lat·i·tu·di·nal·ly adverb
[latitude illustration]


Main Entry: lon·gi·tude
Pronunciation: 'län-j&-"tüd, -"tyüd, British also 'lä[ng]-g&-
Function: noun
Etymology: Middle English, from Latin longitudin-, longitudo, from longus
Date: 14th century
1 a : angular distance measured on a great circle of reference from the intersection of the adopted zero meridian with this reference circle to the similar intersection of the meridian passing through the object b : the arc or portion of the earth's equator intersected between the meridian of a given place and the prime meridian and expressed either in degrees or in time
2 archaic : long duration
[longitude illustration]

Forget the globe spinning, your head is spinning, right? I'm sure you've had worse spins. Fight the spin and keep reading.

Here's the same information in pictures, stolen (again) this time from WWWebster's. If you can't see these pictures for some reason, use the links provided at the end of each definition above.

latitudeillus.gif (9372 bytes)

Latitudes are the lines, called parallels, that run like a circle around the globe in the same direction as the equator.All of these lines are parallel to each other, they never cross.  The equator is a parallel of latitude. Remember that the equator is a parallel of latitude and you'll never have a problem. One more thing: the equator is zero (0) latitude. What's the latitude of the north pole?

Here's longitude in an illustration, courtesy of WWWebster:

longitudeillus.gif (10577 bytes)

Pretty, huh? Like a bird cage almost. Longitudes are the lines that run "up and down", converging at the poles. Remember that lines of longitude run the "long" ways, the opposite of latitude, through the poles, almost the same direction as California coast, whatever it takes and you'll be fine.

Still with me? If you're not, if you can't identify a parallel of latitude from a line of longitude, then go back and study those two figures again. Because it gets a little more complicated from this point on.

I mentioned above that the equator is zero (0) latitude. To say it more accurately, I should have said that the equator is zero (0) degrees latitude. When we divide the globe up into latitudes and longitudes, it's convenient to assign each line of latitude or longitude a degree. The degree symbol looks like this: °.

Degrees are nothing more than a way to divide up a circle (or a sphere) into equal sections. You don't need to know what a degree means mathematically or anything like that. Degrees are a unit of measurement, just like inches or feet or miles (well, almost...).

Refer to the illustration of latitude. As we travel north of the equator, each parallel of latitude (represented as a circle) is assigned a degree between zero (0) and ninety (90). The latitude of the north pole is 90° NORTH, usually represented as N.

Play the same game in the southern hemisphere. What's the latitude of the south pole? If you said 90° S, then you are correct!

In between the equator and the poles, parallels of latitude are divided evenly. Here's a couple simple problems. The answers are at the bottom of the page.

  1. What's the latitude exactly halfway between the equator and the north pole?
  2. What's the latitude exactly halfway between the equator and the south pole?
  3. What's the latitude 1/3 of the way north of the equator?
  4. What's the latitude 1/3 of the way south of the equator?
  5. What's the latitude 2/3 of the way south of the equator? (read carefully, I switched directions here.)
  6. What's the latitude 2/3 of the way north of the equator?

Latitude is a very convenient way to divide up our globe in terms of climate. Sometimes we call these climate zones. You've heard of the tropics? Maybe you've even heard of the Tropic of Cancer or the Tropic of Capricorn. Maybe you've spent a ribald evening above the Arctic Circle in the summer when it doesn't get dark. (Tromsĝ, Norway is a great place to be in the Arctic summer.)

These climate zones are important for understanding a lot about physical and biological processes in the ocean. Memorize these climate zones:

Tropical zone: the region of our planet between 23.5° S and 23.5° N.
Q: What important line of latitude do the tropics contain?

Temperate zone: the region of our planet between 23.5° and 66.5° S and 23.5° and 66.5° N.
Q: What important college does the temperate zone contain?

Polar zones: the region between 66.5° and 90° S and 66.5° and 90° N.
Q: What animal lives in the northern hemisphere polar zone that doesn't live in the southern hemisphere polar zone?

We're not done with latitude yet.

For $100,000 U.S. dollars and a Chevy Malibu, who can tell me what is significant about 23.5°? How about 66.5°?

While I won't give you the answer to that question for a few lectures down the road (and I won't give you the money or the Malibu, either, although if someone wants to sponsor this question, I'll gladly consider it...), I will tell you this: here are some more terms to remember.

Tropic of Cancer: the parallel of latitude at 23.5° N.

Tropic of Capricorn: the parallel of latitude at 23.5° S.

Arctic Circle: the parallel of latitude at 66.5° N.

Antarctic Circle: the parallel of latitude at 66.5° S.

Please note the spelling of Arctic and Antarctic. (Don't forget the "c".)

There's one more convention we need to be aware of. With the advent of computers, navigating according to a N or S wasn't very satisfactory. Computers are particularly reluctant to calculating with letters. For that reason, scientists adopted the system where Northern hemisphere latitudes are given positive values and Southern hemisphere latitudes are given negative values. For example, 30° North latitude is +30°   latitude and 30° South latitude is -30 latitude.

Here's a map that helps illustrate this idea. This map is from NASA's Definition of Latitude and Longitude page:

latlongnasa.gif (6087 bytes)

Note that longitude works the same way, but we'll get to that in a moment.

On a historical note, when people started putting together this system, latitude was pretty easy to figure out. Astronomers had given us an excellent representation of the movement of our planet around the sun and knowing the time of year, one could calculate the angle of the sun at sunrise and noon and figure out position in terms of latitude (don't worry about the details). However, figuring out longitude wasn't so easy.

The "search" for longitude is a fascinating tale of discovery. Dava Sobel's Longitude, published in 1995, offers a "dramatic and riveting" account of the greatest scientific dilemma of the 18th Century. I haven't read it but Rick Lozinsky tells me it's great. If this sort of thing interests you, you might want to take a peek at your local bookstore.


Degrees of longitude are measured from something called the prime meridian or the adopted zero meridian. The dictionary please...

Main Entry: prime meridian
Function: noun
Date: circa 1859
: the meridian of 0 degrees longitude which runs through the original site of the Royal Observatory at Greenwich, England, and from which other longitudes are reckoned

If you are first to do something in science, you get to make the rules (remember, science is about fame, not fortune). So the folks at the Royal Observatory at Greenwich, England, declared their longitude as zero (0). Look at the NASA map above and find 0° longitude. Trace this line up to England. That's the Observatory. (Q: In which climate zone is the Observatory?)

East of the Observatory, line of longitude are given positive values. West of the Observatory, lines of longitude are given negative values. Somewhere they meet.

If you trace a circle to a point exactly opposite from the point at which you started, how many degrees have you traveled? In case you forgot, a circle has 360°. That said, how many degrees is half a circle? That's right, 180°. Find 180° on the NASA map (+ or -, it doesn't matter).

The line of longitude halfway around the world from the Royal Observatory is 180°. Technically, +180° and -180° are the same exact longitudes. What is the name of this most important longitude? Why it's called the International Date Line!

Main Entry: international date line
Function: noun
Date: circa 1909
: an arbitrary line approximately along the 180th meridian designated as the place where each calendar day begins

What do you notice about this definition? Lines of longitude are called meridians. Quick, what are lines of latitude called? (hint: they are parallel)

Look at the NASA map one more time. Try to figure out the approximate latitude and longitude for California. Then go to ZipInfo ( and find the latitude and longitude for your city. Be sure to write it down. Try a few of your favorite cities east or west of where you live and get a feel for their positions in terms of latitude and longitude. Do the coordinates returned by Zip Info make sense?

Crossing the international date line can be quite a trip? Going west across the date line, like I did aboard Calypso, you lose a day. Suddenly, it's tomorrow. Going east across the date line (headed home to California), you gain a day. I actually lived December 23, 1986, twice!

Although they weren't able to get a lock on dates, the Observatory did become the site upon which time is based. Greenwich Mean Time, or GMT, refers to the time of day at Greenwich, England, or the Prime Meridian of the World (as they call it). GMT is also known as Zulu time.

The globe, at 360°, can be conveniently divided into 25 zones. There are 12 zones west of the Prime Meridian (+1 through +12) and 12 time zones east of the Prime Meridian (-1 through -12). Because the United States is east of England, our times zones are "negative" or earlier than England. For example, California, in the Pacific Standard Time (PST) zone is at -8:00 or 8 hours earlier than GMT. Quick, what time is it right now in GMT? Remember, we are earlier, so you need to add 8 hours to figure out the time in GMT, the time it is in Greenwich. Greenwich is in the zero zone, of course.

These time zones can also be designated by letters of the alphabet, which is what the military does (skipping the letter "i" for some reason). In military parlance, Greenwich is the "z" time zone, which they pronounce Zulu.

It's amazing what you are learning in this class, isn't it?

Just for your amusement and possibly for future reference on an exam, here's a listing of all the world's time zones in standard time, courtesy of the city of Greenwich. Daylight's saving time is another thing altogether and there's no need to go into that here, but it is instructive for you to think about these time zones. Here's the web address if you would like to explore their site further, Their millenium preparations are quite extraordinary. You might also want to visit the Map of World Time Zones,

Time Zones of the World:




Civilian Time Zones





GMT - Greenwich Mean
UT or UTC - Universal (Co-ordinated)
WET - Western European
Dublin, Ireland
Edinburgh, Scotland
Lisbon, Portugal
Reykjavik, Iceland
Casablanca, Morocco




WAT - West Africa Azores, Cape Verde Islands




AT - Azores




Brasilia, Brazil
Buenos Aires, Argentina
Georgetown, Guyana




AST - Atlantic Standard Caracas
La Paz




EST - Eastern Standard. Bogota
Lima, Peru
New York, NY, USA




CST - Central Standard Mexico City, Mexico
Saskatchewan, Canada




MST - Mountain Standard.




PST - Pacific Standard Los Angeles, CA, USA




YST - Yukon Standard.




AHST - Alaska-Hawaii Standard
CAT - Central Alaska
HST - Hawaii Standard

EAST - East Australian Standard




NT - Nome.




IDLW - International Date Line West




CET - Central European
FWT - French Winter
MET - Middle European
MEWT - Middle European Winter
SWT - Swedish Winter.
Paris, France
Berlin, Germany
Amsterdam, The Netherlands
Brussels, Belgium
Vienna, Austria
Madrid, Spain
Rome, Italy
Bern, Switzerland
Stockholm, Sweden
Oslo, Norway




EET - Eastern European, Russia Zone 1 Athens, Greece
Helsinki, Finland
Istanbul, Turkey
Jerusalem, Israel
Harare, Zimbabwe




BT - Baghdad, Russia Zone 2 Kuwait
Nairobi, Kenya
Riyadh, Saudi Arabia
Moscow, Russia
Tehran, Iran




ZP4 - Russia Zone 3 Abu Dhabi, UAE




ZP5 - Chesapeake Bay




ZP6 - Chesapeake Bay




WAST - West Australian Standard.




CCT - China Coast, Russia Zone 7




JST - Japan Standard, Russia Zone 8




GST - Guam Standard, Russia Zone 9







IDLE - International Date Line East
NZST - New Zealand Standard
NZT - New Zealand
Wellington, New Zealand
Marshall Islands

Hopefully, your mind is starting to expand a bit. By studying this material, we are building towards a global perspective that will help us better understand ocean processes. To fully comprehend oceanography, you need to think about our planet as a whole. If you can master this global thinking, you are well on your way to success in this course.