# modeling earths surface

## polar coordinate system

You can also use a polar coordinate system. Your location is marked by an angle and distance from some reference point. The angle is usually the angle between your location, the reference point, and a line pointing north. The distance is given in meters or kilometers. To find your location or to move from place to place, you need a map, a compass, and some way to measure your distance, such as a range finder. Suppose you need to go from your location to a marker that is 20o E and 500 m from your current position. You must do the following: Use the compass and compass rose on the map to orient your map with north. Use the compass to find which direction is 20o E. Walk 500 meters in that direction to reach your destination. Polar coordinates are used in a sport called orienteering. People who do orienteering use a compass and a map with polar coordinates. Participants find their way along a course across wilderness terrain (Figure 2.22). They move to various checkpoints along the course. The winner is the person who completes the course in the fastest time.

## globe

Earth is a sphere and so is a globe. A globe is the best way to make a map of the whole Earth. Because both the planet and a globe have curved surfaces, the sizes and shapes of countries are not distorted. Distances are true to scale. (Figure 2.23). Globes usually have a geographic coordinate system and a scale. The shortest distance between two points on a globe is the length of the portion of a circle that connects them. Globes are difficult to make and carry around. They also cannot be enlarged to show the details of any particular area. Globes are best sitting on your desk for reference. Google Earth is a neat site to download to your computer. This is a link that you can follow to get there: http://w tilt your image and lots more.

## conic projection

Instead of a cylinder, you could wrap the flat paper into a cone. Conic map projections use a cone shape to better represent regions near the poles (Figure 2.17). Conic projections are best where the cone shape touches the globe. This is along a line of latitude, usually the equator.

## mercator projection

In 1569, Gerardus Mercator (1512-1594) (Figure 2.15) figured out a way to make a flat map of our round world, called the Mercator projection (Figure 2.16). Imagine wrapping the round, ball-shaped Earth with a big, flat piece of paper. First you make a tube or a cylinder. The cylinder will touch Earth at its fattest part, the equator. The equator is the imaginary line running horizontally around the middle of Earth. The poles are the farthest points from the cylinder. If you shine a light from the inside of your model Earth out to the cylinder, the image projected onto the paper is a Mercator projection. Where does the projection represent Earth best? Where is it worst? Your map would be most correct at the equator. The shapes and sizes of continents become more stretched out near the poles. Early sailors and navigators found the Mercator map useful because most explorations were located near the equator. Many world maps still use the Mercator projection. The Mercator projection is best within 15 degrees north or south of the equator. Landmasses or countries outside that zone get stretched out of shape. The further the feature is from the equator, the more out of shape it is stretched. For example, if you look at Greenland on a globe, you see it is a relatively small country near the North Pole. Yet, on a Mercator projection, Greenland looks almost as big the United States. Because Greenland is closer to the pole, the continents shape and size are greatly increased. The United States is closer to its true dimensions. In a Mercator projection, all compass directions are straight lines. This makes it a good type of map for navigation. The top of the map is north, the bottom is south, the left side is west and the right side is east. However, because it is a flat map of a curved surface, a straight line on the map is not the shortest distance between the two points it connects.

## map coordinates

Most maps use a grid of lines to help you to find your location. This grid system is called a geographic coordinate system. Using this system you can define your location by two numbers, latitude and longitude. Both numbers are angles between your location, the center of Earth, and a reference line (Figure 2.20).

## latitude

Lines of latitude circle around Earth. The equator is a line of latitude right in the middle of the planet. The equator is an equal distance from both the North and South Pole. If you know your latitude, you know how far you are north or south of the equator.

## gnomonic projection

What if want to wrap a different approach? Lets say you dont want to wrap a flat piece of paper around a round object? You could put a flat piece of paper right on the area that you want to map. This type of map is called a gnomonic map projection (Figure 2.18). The paper only touches Earth at one point. The sizes and shapes of countries near that point are good. The poles are often mapped this way to avoid distortion. A gnomic projection is best for use over a small area.

## robinson projection

In 1963, Arthur Robinson made a map with more accurate sizes and shapes of land areas. He did this using mathematical formulas. The formulas could directly translate coordinates onto the map. This type of projection is shaped like an oval rather than a rectangle (Figure 2.19). Robinsons map is more accurate than a Mercator projection. The shapes and sizes of continents are closer to true. Robinsons map is best within 45 degrees of the equator. Distances along the equator and the lines parallel to it are true. However, the scales along each line of latitude are different. In 1988, the National Geographic Society began to use Robinsons projection for its world maps. Whatever map projection is used, maps help us find places and to be able to get from one place to another. So how do you find your location on a map?

## map projections

Earth is a round, three-dimensional ball. In a small area, Earth looks flat, so it is not hard to make accurate maps of a small place. When map makers want to map the round Earth on flat paper, they use projections. What happens if you try to flatten out the skin of a peeled orange? Or if you try to gift wrap a soccer ball? To flatten out, the orange peel must rip and its shape must become distorted. To wrap around object with flat paper requires lots of extra cuts and folds. A projection is a way to represent Earths curved surface on flat paper (Figure 2.14). There are many types of projections. Each uses a different way to change three dimensions into two dimensions. There are two basic methods that the map maker uses in projections: The map maker slices the sphere in some way and unfolds it to make a flat map, like flattening out an orange peel. The map maker can look at the sphere from a certain point and then translate this view onto a flat paper. Lets look at a few commonly used projections.

## types of maps

There are many other types of maps besides road maps. Some examples include: Political or geographic maps show the outlines and borders of states and/or countries. Satellite view maps show terrains and vegetation forests, deserts, and mountains. Relief maps show elevations of areas, but usually on a larger scale, such as the whole Earth, rather than a local area. Topographic maps show detailed elevations of features on the map. Climate maps show average temperatures and rainfall. Precipitation maps show the amount of rainfall in different areas. Weather maps show storms, air masses, and fronts. Radar maps show storms and rainfall. Geologic maps detail the types and locations of rocks found in an area. These are but a few types of maps that various Earth scientists might use. You can easily carry a map around in your pocket or bag. Maps are easy to use because they are flat or two-dimensional. However, the world is three- dimensional. So, how do map makers represent a three-dimensional world on flat paper?

## map legends

Look for the legend on the top left side of the map. It explains how this map records different features. You can see the following: The boundaries of the state show its shape. Black dots represent the cities. Each city is named. The size of the dot represents the population of the city. Red and brown lines show major roads that connect the cities. Blue lines show rivers. Their names are written in blue. Blue areas show lakes and other waterways the Gulf of Mexico, Biscayne Bay, and Lake Okeechobee. Names for bodies of water are also written in blue. A line or scale of miles shows the distance represented on the map an inch or centimeter on the map represents a certain amount of distance (miles or kilometers). The legend explains other features and symbols on the map. It is the convention for north to be at the top of a map. For this reason, a compass rose is not needed on most maps. You can use this map to find your way around Florida and get from one place to another along roadways.

## maps as models

Imagine you are going on a road trip. Perhaps you are going on vacation. How do you know where to go? Most likely, you will use a map. A map is a picture of specific parts of Earths surface. There are many types of maps. Each map gives us different information. Lets look at a road map, which is the probably the most common map that you use (Figure 2.13).

## using latitude and longitude on a map

If you know the latitude and longitude of a place, you can find it on a map. Simply place one finger on the latitude on the vertical axis of the map. Place your other finger on the longitude along the horizontal axis of the map. Move your fingers along the latitude and longitude lines until they meet. For example, say the location you want to find is at 30o N and 90o W. Place your right finger along 30o N at the right of the map. Place your left finger along the bottom at 90o W. Move your fingers along the lines until they meet. Your location should be near New Orleans, Louisiana, along the Gulf coast of the United States. What if you want to know the latitude and longitude of your location? If you know where you are on a map, point to the place with your fingers. Take one finger and move it along the latitude line to find your latitude. Then move another finger along the longitude line to find your and longitude.

## longitude

Lines of longitude are circles that go around Earth from pole to pole, like the sections of an orange. Lines of longitude start at the Prime Meridian. The Prime Meridian is a circle that runs north to south and passes through Greenwich, England. Longitude tells you how far you are east or west from the Prime Meridian (Figure 2.21). You can remember latitude and longitude by doing jumping jacks. When your hands are above your head and your feet are together, say longitude (your body is long!). When you put your arms out to the side horizontally, say latitude (your head and arms make a cross, like the t in latitude). While you are jumping, your arms are going the same way as each of these grid lines: horizontal for latitude and vertical for longitude.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

distance north or south of the equator

``````a. conic map

b. coordinates

c. gnomonic map

-->  d. latitude

e. longitude

f. projection

g. Mercator projection
``````

Lines of latitude give the distance north and south of the

``````a. Prime Meridian

-->  b. Equator

c. North Pole

d. South Pole
``````

map made by projecting one point on Earth onto a flat surface

``````a. conic map

b. coordinates

-->  c. gnomonic map

d. latitude

e. longitude

f. projection

g. Mercator projection
``````

A Mercator projection

``````a. is a perfect likeness of Earth

b. uses a cone to create the map

-->  c. distorts the size of continents near the poles the most

d. distorts Mexico more than Greenland
``````

map made by projecting Earths surface onto a cylinder

``````a. conic map

b. coordinates

c. gnomonic map

d. latitude

e. longitude

f. projection

-->  g. Mercator projection
``````

Which is NOT true on a map legend?

``````a. Blue is used to show water features

-->  b. Purple lines show major roads

c. Black dots represent cities

d. The size of a city dots helps to show its population
``````

Which is NOT true of a Robinson projection?

``````-->  a. It is a completely accurate map with no distortions

b. It is more oval than rectangular

c. It is more accurate in size than the Mercator

d. It was created using mathematical formulas
``````

map made by projecting Earths surface onto a cone

``````-->  a. conic map

b. coordinates

c. gnomonic map

d. latitude

e. longitude

f. projection

g. Mercator projection
``````

distance east or west of the prime meridian

``````a. conic map

b. coordinates

c. gnomonic map

d. latitude

-->  e. longitude

f. projection

g. Mercator projection
``````

Which is NOT true of the Prime Meridian?

``````a. It is a line of longitude

b. It runs through Greenwich, England

c. It is known as 0 degrees

-->  d. It runs from east to west
``````

numbers in a grid that locate a particular point

``````a. conic map

-->  b. coordinates

c. gnomonic map

d. latitude

e. longitude

f. projection

g. Mercator projection
``````

any method of representing Earths curved surface in two dimensions

``````a. conic map

b. coordinates

c. gnomonic map

d. latitude

e. longitude

-->  f. projection

g. Mercator projection
``````

All map projections have some disadvantage.

``````-->  a. true

b. false
``````

Both Robinson and Mercator Projections have distortion at the poles more than at the equator.

``````-->  a. true

b. false
``````

Gnomonic projections are most accurate when used for small geographic areas.

``````-->  a. true

b. false
``````

The Mercator Projection, unlike most other maps, represents the world with South at the top of the map.

``````a. true

-->  b. false
``````

A globe is the most detailed map we have of Earth.

``````a. true

-->  b. false
``````

The top of a map generally represents north.

``````-->  a. true

b. false
``````

A geographic map shows types and locations of rocks in an area.

``````a. true

-->  b. false
``````

Mercator projections are no longer used today.

``````a. true

-->  b. false
``````

On a Mercator projection, landmasses near the poles are reduced in size.

``````a. true

-->  b. false
``````

The poles are often mapped with gnomonic projections to avoid distortion.

``````-->  a. true

b. false
``````

A Robinson projection is more accurate than a Mercator projection.

``````-->  a. true

b. false
``````

Lines of latitude meet at the poles.

``````a. true

-->  b. false
``````

Lines of longitude are all parallel to one another.

``````a. true

-->  b. false
``````

You can find your location on a map if you know only your latitude and longitude.

``````-->  a. true

b. false
``````

Distances are true to scale on a globe.

``````-->  a. true

b. false
``````

Types of maps include

``````a. relief maps.

b. climate maps.

c. geologic maps.

-->  d. all of the above
``````

The Mercator projection was invented in the

``````a. 1300s.

-->  b. 1500s.

c. 1700s.

d. 1900s.
``````

A map in which all the lines of latitude and longitude are straight lines is a

``````a. gnomonic projection.

b. Robinson projection.

-->  c. Mercator projection.

d. conic projection.
``````

Which type of map would you use if you wanted a very accurate representation of a tiny part of Earths surface?

``````a. conic projection

-->  b. gnomonic projection

c. Mercator projection

d. Robinson projection
``````

You know whether a place is in the northern or southern hemisphere based on its

``````-->  a. latitude.

b. longitude.

c. projection.

d. prime meridian.
``````

Which coordinates represent a location within the continental United States?

``````-->  a. 35 N, 95 W

b. 35 S, 95 W

c. 35 N, 95 E

d. 35 S, 95 E
``````

To move to a location that is 4 meters west of your current position, you would need a

``````a. compass.

b. metric ruler or tape.

c. Mercator projection.

-->  d. two of the above
``````

## diagram questions

No diagram questions associated with this lesson