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Maps and GIS


Outline

  1. Introduction
  2. Latitude and Longitude
  3. Projections
  4. Thematic maps
  5. Scale
  6. Generalization
  7. Geographic Information Systems

o        Definition

o        Applications

o        Future Developments

  1. References
  2. Review Questions

Introduction

The purpose of a map is to show the world at a smaller scale so that we are able to get a sense of where things are located in relation to one another, and that we can have a better understanding of different patterns in geographical space.

The first known map has been dated to approximately 2500 B.C.E. and was found in Babylonia or present day Iraq. The map was drawn on a clay tablet in cuneiform style and showed land boundaries most likely used to keep peace among landowners. However, many believe that the first map was drawn much earlier, perhaps drawn in the sand as a representation of the surrounding landscape.
 
Mental maps were the first maps. These maps are formed in our heads. We form mental maps from two sources of information: 1) they are a direct perception of the environment where we live, and 2) they appear from maps that have been drawn previously. We all have a mental atlas of shapes of states and countries. Mental maps come into play everyday. We use our mental maps when we walk around campus to find where our next class is or when we are driving in the city.
 
From 250 B.C. to 100 C.E., the Greeks made major advancements in understanding how to represent the world. Two specific individuals, Eratosthenes and Ptolemy, greatly contributed to geography and cartography. Eratosthenes wanted to determine the circumference of the Earth. Around 250 B.C.E., knowing that the city of Aswan in Egypt knowing that the city had perfectly perpendicular rays of the sun on a particular day, he determined the angle of inclination further north in Alexandria to be seven and one half degrees -- about 1/50th of a circle (360 degrees).  Then he found the distance of the two cities (Alexandria and Aswan) to be 500 miles. He then multiplied the distance between the two cities to arrive at an Earth's circumference of about 46,000 km. The actual measurement is 40,000 km, or 25,000 miles. These calculations would be lost from 300 C.E. to 1400 C.E. Ptolemy, however, probably made the most important contributions to cartography.

Ptolemy developed a book titled Geographia that held all the knowledge the Greeks learned about the Earth. He also suggested a map projection system and a way to section the Earth to create larger scale maps. In sectioning the Earth, Ptolemy is the founder of latitude and longitude.
 
Although the abundance of map knowledge was growing, many beliefs about the Earth were lost in the Dark Ages.  In the Renaissance in the 1400s, some of the Greek writings had been found. Ptolemy's Geographia was one of those documents and was widely distributed in printed form and became "the bible" for all explorers in the 1400s.

Latitude and Longitude

Latitude and longitude are lines that are used to help represent a spherical coordinate system.  A spherical coordinate system is a 3D extension a flat coordinate system (e.g., cartesian or polar).  The x-axis appears horizontally and the y-axis appears vertically.  Lines of longitude correspond to coordinates along the x-axis and measure how far east or west you go from the Prime Meridian.  Lines of latitude (corresponding to the y-axis) measure how far north or south from the Equator.

Lines of latitude (or parallels) are measured from zero to ninety degrees north or south of the equator. The equator is at zero degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of longitude go from 180 degrees east or west of the Prime Meridian, which is at zero degrees longitude. Lines of latitude are parallel and get shorter as they approach the poles, while Lines of longitude converge at the poles and are the same length. If you follow the equator, one degree is approximately equal to sixty-nine miles. This only occurs on the equator. The distance between a degree of longitude at 60 degrees north or south of the equator, is half of 69 miles.

Since latitude and longitude lines are invisible lines going around the Earth, finding the lines of longitude was difficult for sailors. The chronometer was then invented to help determine lines of longitude and is like a clock. Lines of latitude were measured by the angle to the horizon and a star using a sextant.

The Prime Meridian passes through the Greenwich Observatory in England.  It is considered zero degrees in terms of longitude.  The Prime Meridian intersects with the Equator just off the coast of Africa. This point is 0 degrees latitude and 0 degrees longitude.

Projections

Although map projections are very useful, they can also create some major problems.  It is impossible to transform a round surface to a flat surface without introducing distortion.  Many map projection models have been made, each with own characteristics, that distort the Earth in some fashion. In fact, all maps distort distance.

Conformal maps project the round earth to a flat surface, by preserving angles over small areas but distorting area. On a conformal map, Greenland looks enormous. An example of this would be a Mercator projection. Greenland appears to look the same size as Africa, when in reality, Greenland is much smaller than Africa, but due to the style of projection there is distortion near the poles.  Mercator designed this in the kind of map projection in the 1500s. The Mercator map is basically formed by wrapping a cylinder around a globe and then flattening it out. These maps, however, were very useful to sailors because they could easily be used with a compass. Another important feature on the Mercator projection that helped sailors, are that lines of latitude intersect at right angles.
 
Equal area maps are opposites of conformal maps in the sense that they preserve area correctly, but distort angles greatly.  This projection is greatly identifiable because the map is rounded and the lines of latitude and longitude are curved.
 
The graticule is a system of latitude and longitude that defines a grid on the Earth's surface. On a conformal projection, lines of latitude and longitude meet at right angles. Also, the area between lines of latitude and longitude do not decrease consistently between the equatorial and Polar Regions.

Thematic maps

The difference between thematic maps and general reference maps is described by the phrase “in place, about space.” This means that general reference maps show where things are located “in space” and thematic maps depict patterns “about space.”

The function of thematic maps is to convey patterns of distribution, while a general reference map puts features “in space.” Examples of thematic maps include maps showing the population density, life expectancy, or demographic trends.

Scale

Scales are relationships between the distance on the map and the actual distance on the earth.  A scale with two different units must be verbally reported. For example, the scale 1 cm: 10 km means that 1 centimeter on the given map is equal to 10 kilometers in the real world. An example of an English verbal scale is 1 in: 10 mi, meaning 1 inch on the given map represents 10 "real world" miles.

The representative fraction is another way of expressing scale on a map. A scale of the form 1:24000 is a representative fraction. This fraction must be expressed in the same units. For example, for every 1-inch on the map, there is 24000 inches on the surface of the Earth.

Some major conversions to know are: 1 mile = 63360 inches, 1 mile = 5280 feet, 1 foot = 12 inches. In the metric system, 100,000 cm = 1 km, 100 cm = 1 m, 1000 m = 1 km. 

Generalization

Maps are generalizations of reality. This means that, depending on scale, many features do not appear on a map. Even large features are sometimes left out. For example, the city of Baltimore is often not included on a page-size map of the U.S. This is because other cities around it are so large that there is no room to feature Baltimore on the map. Omaha, on the other hand is usually included on such a map, even though it is a much smaller city than Baltimore.

If you are traveling to Kearney, the location on the map isn't quite correct. Since the city of Kearney is so close to Interstate 80, the width of the interstate line on the map would be running right over the city. So the point where Kearney is on the map is moved a little to the north. Other roads heading into Kearney also need to be moved. Spatial relationships are conserved however. 

Maps are also valuable in that they are useful for gaining knowledge of patterns in geographic space and expanding our understanding of navigation. They are important to show trends in things as weather, population and growth. They are a visual source where spatial messages are transmitted from a cartographer to everyday people like you and me.

Geographic Information Systems

Geographic Information Systems, or GIS, is a computerized mapping system. GIS can be used for storing, editing, analyzing, and sharing maps. The first GIS system was developed in 1964 in Ottawa by Roger Tomlinson. GIS technology uses digital information in which digital data is created. A map or survey plan is transferred into a CAD (computer aided drafting) program to produce a digital piece of information.

 

GIS has many different applications. A very convenient tool that GIS allows you to do is create map layers and overlays. Using this procedure, a cartographer can compare different cultural aspects such as population densities, birth rates, life expectancy, etc. to find similarities and differences. GIS can also be used to keep track of gas pipelines, electric lines, and roads. You can also use this system to help determine new city developments.

 

The future looks bright for GIS Many students have started taking classes to help familiarize them with the new mapping techniques used in GIS as the job market is expanding for this type of training. GIS now is getting into location-based services or LBS. LBS lets GPS devices display their location in relation to various items (e.g. schools, restaurants, hotels). GIS is also a forerunner in aiding with online map services like Google Earth, MapQuest, and Rand McNally. A new development is the addition of time. The condition of Earth’s surface and atmosphere can be observed through a feeding satellite into a GIS. This allows researchers to observe vegetation in relation to weather over days, months, and years.

References

Clawson, David L.; Haarmann, Viola; Johnson, Douglas L.; and Johnson, Merrill L. World Regional Geography: A Developmental Approach. 2007. Pearson Prentice Hall. Upper Saddle Creek, NJ.
Hobbs, Joseph J., and Salter, Christopher L. Essentials of World Regional Geography. 2006. Thomson Higher Education. Belmont, CA.
Pulsipher, Lydia Mihilic. World Regional Geography. 1999. W.H. Freeman and Company. New York.

 


Review Questions

1.Which of the following representative fractions is equivalent to a scale of one inch to one mile? A. 1:13,360; B. 1:23,360; C. 1:93,360; D. 1:63,360. E. none of the above.
 
2. The measurement of the earth's circumference: A. was not undertaken until the 1400's; B. was done by Eratosthenes around 250 B.C.; C. required knowing the distance to the middle of the earth; D. was accomplished by contemporaries of Columbus; E. was miscalculated by Columbus.

3. A map with a representative fraction of 1:24000 could be interpreted as: A. 1 inch represents 24000 miles; B. 1 cm represents 24000 KM; C. 1 inch represents .24 miles; D. 1 mile represents 24000 miles.

4. Mental maps: A. are derived from direct experience with the environment; B. are derived from maps; C. are useful in organizing information; D. all of the above.

5. The important geographical direction line that passes through the Greenwich Observatory near London is: A. the prime meridian; B. 180 degrees north latitude; C. the equator; D. the international date line; E. none of the above.

6. The Greek Eratosthenes measured the earth's circumference: A. to within about 6000 KM; B. performed his calculations around 250 B.C.; C. measured the angle of the shadow cast by a pole; D. measured the difference in the sun's angle of inclination between the present-day cities of Alexandria and Aswan, Egypt; E. all of the above.

7. If there are 63,360 inches in a mile, how many miles are represented by one inch on a 1:24,000 scale map? A. 0.378 miles; B. 2 miles; C. 2.64 miles; D. 5.28 miles; E. none of the above.

8. On the Mercator projection: A. lines of latitude and longitude do not meet at right angles; B. areas are represented correctly; C. Greenland is depicted as being larger than Australia while the opposite is true; D. angles are not represented correctly on any part of the map excluding the equatorial region; E. all of the above.

9. Mental maps: A. are a form of mental image; B. are probably very accurate but cannot be drawn very well by most people; C. can be the layout of a building or a map of the world; D. are derived through direct experience with the environment and through maps; E. all of the above.

10. Lines of latitude: A. begin with the prime meridian; B. are designated by being East or West from an origin; C. are of equal length; D. become shorter away from the equator; E. none of the above.

11. All of the following are correct statements about map projections, except: A. transforms the round surface to a flat surface; B. were originally created by projecting a translucent globe onto a wall; C. it is geometrically impossible to transform a round surface to a flat surface without introducing distortion; D. always preserve distance relationships between all points on the map; E. equal-area map projections preserve area relationships.
 
12. All of the following are true statements about longitude, except: A. has its origin at the prime meridian; B. extend east and west to 180 degrees longitude; C. are relatively equal in length; D. could be determined by sailors using a device called the sextant; E. could not be determined by sailors until the introduction of the chronometer.
 
13. How many degrees of a full circle can you travel eastward or westward from the zero (prime) meridian before heading back toward the Prime Meridian? A. 60deg. B. 90deg. C. 360deg. D. 180deg. E. none of the above.
 
14. 0deg. longitude and 0deg. latitude is located: A. over central Australia; B. in Brazil; C. in the Atlantic south and west of Africa; D. at the South Pole; E. none of the above.
 
15. To find longitude, a sailor needs to know: A. the elevation of the sun above the horizon; B. the latitude at the prime meridian; C. local time and the time at another line of longitude; D. the relative space; E. none of the above.
 
16. A map projection transforms the spherical earth to a flat surface. There are literally thousands of different projections. Gerhard Mercator developed one of the first projections in 1569 in what is now the Netherlands. The Mercator projection: A. preserves angular relationships but distorts area; B. distorts distance but preserves area relationships; C. preserves distance but distorts angular relationships; D. distorts distance and angular relationships; E. none of the above.
 
17. Latitude and longitude is a spherical coordinate system with its origin at 0deg. latitude and 0deg. longitude. This point is in the Atlantic Ocean just below the African country of the Ivory Coast. Locations are measured in degrees away from this origin in north, south, east, and west directions:  23.34deg. S and 46.38deg. W is probably located in: A. Russia; B. Canada; C. South Africa; D. South America; E. none of the above.
 
18. The circumference of the earth at the equator or along any line of longitude is approximately: A. 25,000 KM; B. 40,000 KM; C. 36,000 KM; D. 46,000 KM.

19. Which of the following represents the ratio of the distance between two places on a map and the actual distance between those two places on the Earth's surface? A. scale; B. key; C. fraction; D. coordinates.

20. What is G.I.S.? A. a location tracker. B. computerized mapping system. C. a device used to located longitude. D. a group of maps.


Originally submitted by Heather Aller on 2-1-96. Re-submitted by Jennifer Anderson on 2/6-97. Re-submitted by Dave Caplinger on 6/14/97.  Re-submitted by Jason Altman on 12/1/00. Re-submitted by Mike Golka, Frank Hebert, Andrew Trent, Camren LeFlore, and Charles Quigley on 4-9-07.