*Preparing Your Child for Map Work*
Laying the Foundation
By: Green

If you've ever watched scouts, hikers, military or rescue groups working with GPS units and wished YOU knew how to do that, here is a very basic starting point, understanding the system upon which this knowledge is based. Read on to lay a most basic foundation....

The earth is a sphere (ball) that revolves on its axis once a day. The axis is an invisible line that runs from the North Pole, through the center of the earth, to the South Pole. The earth spins on its axis like a set of wheels spin on an axle. Think of a simple car toy.

The equator is an invisible band that circles the center of the earth at its greatest circumference. This is the point at which the sun's rays hit most directly and is the hottest area on earth. By contrast, the poles are further from the sun's direct rays and are the coldest areas on the earth.

The earth can be divided into hemispheres of significance.  The most useful divisions are the Northern and Southern Hemispheres and the Western and Eastern Hemispheres. The Northern and Southern hemispheres are separated by the equator. From the North Pole down to the equator is the Northern Hemisphere and from the South Pole up to the equator is the Southern Hemisphere. The Eastern and Western hemispheres are divided by an invisible line that goes around the earth at a right angle to the equator. This line (or meridian, meaning big circle) passes through the north and south poles and cuts the earth in half as east and west. It crosses directly through a place in London, England called the Greenwich Observatory (pronounced grin' itch) and is called the Prime Meridian. Everything on the half to the west of Greenwich is the called the Western Hemisphere. Everything to the east of the observatory is in the Eastern Hemisphere. The North American continent, for instance, is in the Western Hemisphere, which is why we are called 'western nations'. Russia and China, for instance, are in the Eastern Hemisphere and as such are considered 'eastern' nations.

To be able to locate yourself at any one point on earth, a grid system was devised to give a 'number' to every area on the earth. This number could get you within less than a mile from your location and even closer if you had more sensitive (longer) numbers. If you could imagine the face of a clock, it is divided into 12 portions (1-2-3-4-5...) to represent hours on the clock. Each of these hour divisions is further divided into minutes, so now you have 60 little hash marks around your clock face, each representing a minute. Though we don't do it, we could actually put in very tiny hash marks between each minute to divide it into seconds. If we did, that would give us a clock face with 3600 hash marks around it! That would be too crowded to read however, so we limit our clock markings to hours and minutes. A compass looks very similar to a clock face and is used to divide up a circle much in the same way a clock divides up minutes and hours on a clock face. A compass divides a circle into 360 equally spaced slices, like if you cut a pizza into 360 slices! Each slice is called a degree (just like the word for temperature). One 'degree' is like getting 1 slice of that pizza that was cut into 360 slices.

Now, imagine cutting an orange into quarters with a knife. If you want the best cut, you cut through the top where the stem attached to the orange, straight down through to the bottom. (By the way, if that were the earth, you would have just created an east and west hemisphere.) If you wanted 4 slices, you could cut each half into halves from top to bottom, just as you did originally, and you'd have 4 slices. Imagine cutting an orange into 360 slices! Wow! That would be one heck of a small sliver you would get! Anyway, the earth is divided into 360 slices also and each is called one degree. If instead of cutting the orange, you just drew the lines where you wanted to cut, you'd have something similar to the lines on a globe. But... just like with a clock face, it gets pretty crowded if you put every second on the clock, so, we put every fifth or tenth or twentieth degree line on the orange (or the globe). These circles you've drawn on the orange, had you drawn them on a globe would be called 'meridians', which means, big circles.

To be of use for finding yourself on the earth, you would need to give these meridians numbers. So, some clever people decided to designate one spot as the beginning, and as with a clock or a number line, you don't start with number one, you start with zero. The first (or Prime) meridian is 0 degrees. The next one is 1 degree, then 2 degrees, then 3 degrees, all the way up to 180 degrees. Instead of going all the way around with higher numbers, they did the same thing on the other side. It follows also with 1 degree, then 2 degrees, then 3 degrees all the way up to that same meridian called 180 degrees. At first it seems confusing on why anyone would try to help you by calling opposite sides of the globe by the same numbers, but to clarify EXACTLY which 'hemisphere' you are in, they call one side 1 degree West and the other side, 1 degree East. Without even looking at a globe, you could know if you were in the Eastern or Western Hemisphere by knowing the number and its corresponding letter.

When I say it is 1:00, I am telling you the time. I am measuring how much time has elapsed since it was midnight. When I say someone is at 100 degrees west, I am telling you his 'longitude', the distance that has passed between them and the 'prime' meridian (the first one, at zero degrees). This is a measure of distance as you travel around the globe from east to west. What seems so funny is that the lines on the globe for measuring the distance from east to west all go north and south! The reason they did this is because with the earth being round, you can't just say, "I've gone 100 miles from the prime meridian, so I must be at 100 degrees west." Because if you go 100 miles from the prime meridian starting at the equator and a friend goes 100 miles west from the prime meridian up in the Arctic Circle, you would end up at different meridians. Imagine that sliced orange again, the tops are pointed and the middles are wide. The globe is the same way. Similarly, the meridian lines will be wider at the equator and touching at the north and south poles. Longitude is the measure of how many degrees you have traveled east or west from the Prime meridian to your current location. The 180 degree meridian connects every place on earth from up in the north pole to down at the south pole that is 180 degrees away from the Prime meridian. That is why the lines go from north to south to tell you the longitude.

Now that you know how to measure your location going east or west, let's look at determining your position going north and south. If you start at the equator and move to the North Pole, you are measuring 'latitude'. Same if you measure your location from the equator to the south pole. Now you are measuring distance from the equator. Since you are only measuring from the equator to a pole, you are only looking at a quarter of a circle, which is 90 degrees.  If you go 10 degrees north of the equator at any point on earth, it is called 10 degrees north latitude. If you go 10 degrees south of the equator at any point, that is called 10 degrees south latitude. The lines marking the latitude actually are not like the lines for longitude at all. These lines are parallel to each other and parallel to the equator. As such, they are called parallels. The circles get progressively shorter as you approach the poles. The parallels that tell you how far north or south you have gone actually go from east to west on a globe. That is because, if you draw a dot on every place on earth that is 10 degrees (or 20, or 30...) north of the equator and then connected them all with a line, they'd run from east to west, not north to south. The equator would be at 0 degrees latitude. The North Pole would be at 90 degrees latitude NORTH. The South Pole would be at 90 degrees latitude SOUTH.

Because latitude lines parallel, you can measure a preset distance between them and it will always be the same. There is approximately 69 miles between each degree of latitude. In addition, if 69 miles distance between latitudes is too far for you to find your home on a map, you can divide degrees in to minutes. One degree of latitude can be divided into 60 minutes which equals 1 nautical mile (approximately 1.15 land miles) and each minute has 60 seconds (same words used for telling time.)  When writing a place's location in latitude and longitude, always write the latitude first.

If you pull out a globe or a map, look to see if the lines of latitude and longitude are marked. If so, try and find your city on the map or globe and write down the coordinates of your home. For practice, try locating these coordinates on your map or globe. Before you look, guess which hemispheres to look in, north versus south and east versus west. Answers can be found below. (No peeking until you try!)

1. 30 degrees N / 105 degrees E
2. 20 degrees S / 135 degrees E
3. 40 degrees N / 105 degrees W
4. 60 degrees N / 15 degrees E
5. 30 degrees N / 0 degrees
6. 30 degrees S / 60 degrees W

This should get you up to speed on the basics needed to move on to map and compass work.

Good luck and have fun!

1. China
2. Australia
3. Denver
4. Sweden
5. Algeria
6. Argentina


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