TOUR OF A TOPO Copyright GeoQuest Publications

Transcription

1 Objective TOUR OF A TOPO Copyright GeoQuest Publications 1 The student will demonstrate how to use the information on a topographic map to 1) determine the name, location, and source of a quadrangle map, 2) determine the names of adjacent maps in the series, 3) describe the differences in roads using the map s legend, 4) determine the map s scale, 5) describe and define contour lines and how to find an index contour, 6) describe the difference between True North and magnetic north and how to find the map s declination, 7) determine latitude, longitude, and universal transverse mercator (UTM) coordinates on a map, and 8) describe how to use the Public Lands Survey System to find a specific location on a topographic map. Method Using the Tour Of A Topo descriptions, the student will learn about the information available on a topographic and will apply this information to answer questions about specific locations on a map. For Teachers of Younger Students 1. Use the Tour Of A Topo map as an overhead transparency. Work through the tour stops as a class, while students follow along on their copies of a real topographic map. Eliminate the details that are too difficult for younger students to absorb. 2. Modify the list of questions to meet the needs of younger students. Call specific attention to familiar landmarks. Materials * Copy of Tour Of A Topo map guide for each student * Local topographic map for each pair of students. Note To Teacher: A topographic map of your local watershed works best for this exercise as students relate well to familiar landmarks and place names. Local topographic maps are available from the US Geological Survey (USGS) at USA-Maps. An index of Oregon topographic maps is also available from the USGS. The index can help you quickly decide which maps are available for your area. You can also obtain topographic maps from local sporting good outlets and map stores. Expect to pay $6.00 to $7.00 per map (1999 prices). Laminate the maps to extend their use. If students are to mark on the laminated maps, use water-based felt marker pens. Maps are easily wiped clean with damp paper towels and are quickly available for the next class use.

2 Map symbols used on most topographic maps are not discussed in this activity. The USGS also produces a chart of symbols which is helpful for students involved in map work. Ask for a symbol chart when requesting maps from USGS. Earth-Science textbooks often have USGS Topographic map legends in their appendix. The questions at the end of this activity can be used as a worksheet as students work through the exercise or it can serve as a measure of understanding (or quiz) following the activity. Background Do You Know... how to use a map? Do you know how to give a legal description of your school s location or maybe your Dad s favorite fishing hole? Do you know how to obtain the elevation of your favorite ski slope or how to determine the scale of distance a map covers? A map provides a wealth of information and with a little practice you can access this information to find out all kinds of things about your local watershed. You can learn a lot by looking at the information outside of your map s boundaries as well as inside. The first essential step in getting to know your watershed is to obtain a map of it. But, a map isn t a lot of help if you do not know how to use it. Maps are the common ground among all the players in a watershed study. and are important communication tools if working with a number of groups in the same watershed. Each of you needs a copy of the same map, so you can all talk the same language and maintain the same points of reference. Maps are a permanent record of your watershed. You can mark your study sites, important reference points, restoration work sites, land use designations, pollution sources, historical sites, or a number of other important locations that are part of your watershed study. 2 Procedure Now It s Your Turn... Just what can you learn from a map. Join us for a Tour Of A Topo and find out. Working in pairs, use your Tour Of A Topo tour guide and a local topographic map to explore the dimensions of a map and your watershed. After completing the tour, answer the questions at the end of the exercise.

3 Tour Of A Topo 3 Latitude UTM Grid # s Latitude 9 United States Department of the Interior Geologic Survey Willamette Meridian Longitude Name of Quadrangle Location of Map Topographic Map Series Longitude 1 Start Tour Here 8 UTM Grid # s 10 Township 1 S Township 2 S (Adjacent Map) 2 Latitude UTM Grid # s Latitude 7 Longitude Range 1 W Range 1E Magnetic Declination 6 Scale 4 Contour Interval 5 Road Legend Name of Quadrangle Edition Date 3 Revision

4 TOUR OF A TOPO 4 Our Tour begins in the upper right hand corner of the topographic map. First we will travel around the outside of the map (clockwise) and then venture to the inside with occasional stops noted by a number. Stop 1 Name, Location, Series The name of the quadrangle usually reflects a prominent feature in the area--a town, city or a physical feature such as a mountain or a lake. These are called quadrangle maps because the maps have four equal sides in terms of degrees latitude and longitude. However, one quickly realizes that the map length is different than its width. Remember that the earth is three dimensional and the map is two dimensional. The length of a degree of latitude is about the same throughout the world. Latitude lines are parallel to the equator, run east-west and are measured in degrees north and south of the equator. The length of a degree of longitude varies with distance from the equator. Longitude lines converge at the poles, run north-south and are measured east and west of the prime meridian that runs through Greenwich, England (see the globe below and the chart on the next page). A topographic map purchased for a parcel of land straddling the equator (Puerto Rico) would be almost square. As you move away from the equator the map begins to resemble a rectangle. A 7 1/2 minute topographic map may be distorted as much as 5%. Because the maps in the United States are based on the Lambert Conic Equal Area Projection, distortions are minimized. Longitude (80 W Meridian) North Geographic Pole (True North) Latitude (40 N Parallel) Equator (0 Latitude) A 7 1/2 7 1/ /2 7 1/2 = degrees = minutes = seconds Prime Meridian (0 Longitude) 15 Quadrangle (size exaggerated)

5 Latitude *Length (miles) of Longitude ** Length (miles) of Latitude very close not close *Length of a degree of arc along the latitude named. **Length of a degree of arc centered on the latitude named. (Table based on the National Geodetic Survey 1980 ellipsoid) 5 The location of the map gives the state and county where the quadrangle is located. Quadrangle maps are published in several sizes, but the two most common are 15 minute quadrangle maps and 7.5 minute quadrangle maps. A 15 minute quadrangle represents an area bounded by 15 minutes of latitude (one-fourth of a degree) and 15 minutes of longitude (one-fourth of a degree). Each 15 minute map can be divided into four 7 1/2 minute maps. 1 = 60 minutes = 3,600 seconds Most all the United States is mapped using the 7.5 minute series at a scale of 1:24,000. A 7 1/2minute quadrangle map covers less area of the earth s surface but shows more detail. Older 15 minute maps can be purchased for some state quadrangles. If you have any questions about Stop #1, a detour to the bibliography or glossary might be in order.. Proceed to Stop #2. Stop 2 Adjacent Map Stop #2 introduces us to an adjacent map that can be purchased if we were to stray from the topographic boundaries of this map. There are typically 8 maps that border any topographic quadrangle map. If the adjacent map (Gladstone #5) is not in parenthesis along the boundary of the map, then the information is included at the bottom of the map. Adjacent Quadrangles OUR MAP 1. Linnton 2. Portland 3. Mt. Tabor 4. Beaverton 5. Gladstone 6. Sherwood 7. Canby 8. Oregon City

6 Stop 3 Legend 6 The symbols used for roads are part of the map s legend. Below the legend appears the name of the quadrangle and the year it was produced. Since maps cannot be updated yearly (a coast range quadrangle in Oregon has not been revised since its production date of 1949), there is often a date of revision. A partial revision results in the revised portion being cast in a different color. Aerial photography is often used when a map is revised. Let s move on to Stop #4. Stop 4 Scale Maps are scale models. To make a model of anything, you must first establish the scale of the model. Scale is the relationship between distance on the map to distance on the ground. A map scale is given in the form of a graphic scale or bar scale, a verbal scale, or a representative fraction. A representative fraction like 1/24000 can be put another way. The 1 could be anything you wish to use as a measuring tool. One of your thumbs on the map would equal 24,000 of your thumbs outside on the ground. One inch on the map would equal 24,000 inches outside. This would be inconvenient because no one measures big distances in inches. If we look at a map whose scale is expressed as a fraction (1/24000), it would indicate that the portion of the earth represented has been reduced to 1/24000 of its actual size. The larger the number, the smaller the scale of the map so less detail is presented. In conclusion, LARGE is small! Some common scales and their verbal equivalents: 1:24,000 1 inch =.379 miles 1:62,500 1 inch =.986 miles 1:250,000 1 inch = 4 miles 1:500,000 1 inch = miles The graphic scale or bar scale below represents a total of two miles. Remember, half the line is one mile. The graphic scale can also be given in kilometers or feet mile Stop 5 Contours and Elevation Topographic maps are scaled-down models of the Earth s three-dimensional surface, printed on a two-dimensional piece of paper. You have seen how the two-dimensional map of length and width can be reduced from the real world to a piece of paper. The third dimension, elevation, is shown on a map using contour lines.

7 A contour line connects map points of the same elevation above sea level. If you were driving along the contour, you would maintain the same elevation above sea level. Different elevations are represented by different contour lines. Every 5th contour line is thicker and called an index contour. Index contours are often marked with an elevation. The maps contour interval is the vertical distance (height) between two adjacent contour lines. The amount of error in the maps elevation can be no more than half of the map s contour interval. If the contour interval on the map is 10 feet, then the elvations have a margin of error (+) or ( )5 feet. Maps with small contour intervals (10 ft) are generally of low relief. Relief is the difference in elevation between two points on a map. Topographic maps of mountainous areas have large contour intervals (50 ft.). If a map has both low and high relief within the topographic quadrangle, there are two contour intervals on the map. By locating the closest labeled contour line and then counting lines, you can determine the elevation of a point. Here are some rules to help you interpret the contour lines on a map. 1. The closer together the contour lines, the steeper the slope. 2. When contour lines cross a stream they form a V that points upstream. 3. Contour lines do not cross unless there is an overhanging cliff. 4. The thicker contour lines are called index contours. 5. All contour lines are multiples of the contour interval. 6. Every point along a contour line has exactly the same elevation. 7. Contour lines can merge to form a vertical cliff. 8. A concentric series of contour lines represent a hill. 9. Depression contours have hachure marks on the downhill side which represent a depression (hole). 10. There is no beginning or end to a contour line. It is an irregularly shaped closed loop. 7 Illustration: Index Contour Stream Elevation 100 Steep Hill Flat 0 Depression (hole) Contour Interval 20

8 Stop 6 Declination 8 The earth has two norths, a magnetic north and a geographic north. A compass responds to the earth s magnetic north which is created by the planet s magnetic core. This magnetic north is not fixed. Because the earth spins on its axis it has a geographic (true) north which is a fixed point at the end of its axis. We sometimes refer to it as the geographic north pole. A topographic map designates direction by referencing the geographic north. It would not be wise to rely on the magnetic north because it slowly wobbles about somewhere to the west of Baffin Island, Canada. Compass direction is revealed with the use of a diagram.. Topographic maps may convey the same information verbally. Designates direction * of geographic north. 19 Is the magnetic declination for the map. * GN MN 19 GN Designates the direction of grid north. (Universal Transverse Mercator System) MN Designates the direction of magnetic north Isogonic Chart showing magnetic declinations Geographic North *(True North) East---Declination---West Magnetic North 35 W 19 E 20 W 15 E 10 W 10 E Based on a USGS map Agonic Line Isogonic lines on a map are lines that show equal declination. The 19 east isogonic line shown above indicates that the magnetic north is slightly east of geographic north. This defines the amount of declination in your area. Local declination can be affected by materials within the earth. Iron in rock can affect your magnetic declination. The agonic line is a

9 9 line that shows no declination as magnetic north lines up with geographic north. This information is used when you want to set your compass and orient your map. Since the magnetic field of the earth changes, isogonic maps are periodically revised. Stop 7 Latitude and Longitude Coordinate In the four corners of the topographic map you will find the degrees longitude and latitude which are used to define the borders of the topographic quadrangle Your Map (45 30 ) is read as 45 degrees and 30 minutes and represents a latitude ( ) is read as 122 degrees, 37 minutes and 30 seconds and represents a longitude. There are 360 degrees in a circle, 60 minutes in a degree and 60 seconds in a minute. We normally think of minutes and seconds as measurements of time. When working with a map, minutes and seconds become fractions of a degree. You will remember from Stop #1 that a degree on a map is a measure of distance. Therefore a fraction of a degree is also a measure of distance. If 1 is equal to approximately 70 miles of latitude, then 30 minutes (1/2 of a degree) is equal to 35 miles. The series of the map explained at Stop #1 can also be determined by subtracting one latitude from the other latitude latitude 7 30 or 71/2 minutes Look at the data table at Stop #1 for 45 latitude and you can determine the number of miles from the top of your map to the bottom of your map with reasonable accuracy. A degree of latitude at 45 north of the equator is equal to miles per degree latitude. 7 1/2 minutes is equal to 1/8 (0.125) of a degree. So 1/8 times miles is equal to 8.63 miles.this number (8.63) gives you the total distance in miles from the top of the map to the bottom of the map. You could check the results by using the graphic scale at Stop #4.

10 Stop 8 UTM Grid 10 The fine blue lines along the borders are the Universal Transverse Mercator (UTM) grid ticks, which are part of an international reference system. Each tick is separated by one kilometer (1000 meters) or about 5/8 of a mile, making it a handy scale. UTM coordinates are commonly used by agencies to locate sampling sites on streams, note locations of culverts, and log other important aspects of the stream. A Global Positioning System (GPS) device helps determine UTM coordinates and can fix latitude and longitude positions. If you are interested in the UTM or GPS system, a detour to the bibliography may be in order. Stop 9 Map Source The United States Department of the Interior s Geological Survey produced the topographic map. An index of Oregon topographic maps is available from the USGS. The index can help you quickly decide which maps are available for your area.you can call the USGS at USA-MAPS. This was a short stop! Lets travel to the interior of the map. Stop 10 Public Land Survey System The U.S. Public Land Survey System divides a region into a township and range grid. The diagram on the next page illustrates this system. The starting points are the Willamette Meridian of longitude and a base line that is surveyed perpendicular to it. The Willamette Stone, located in the West Hills of Portland, Oregon, is at the junction of the Willamette Meridian and the Base Line. Township strips of land run parallel to the base line and are numbered north and south of it (T1N,T1S, etc). Range strips of land run parallel to the Willamette Meridian and are numbered east and west of it (R1E, R1W, etc.). Each intersection of a township strip with a range strip forms a square, called a township. See Public Land Survey map next page.

11 11 Public Land Survey Map Township andrange Grid R4W R3W R2W R1W R1E R2E R3E R4E T 2S R 3W Base Meridian Willamette Line Willamette Stone T3N T 2N T 1N T 1S T 2S T 3S A Township contains 36 Sections NW 1/4 of the NW 1/4 SW 1/4 of the NW 1/4 Lot 1 Lake NE 1/4 of the NW 1/4 SE 1/4 of the NW1/4 N 1/2 SW 1/4 Lot 2 14 Northeast 1/4 West half of SE 1/4 or NE 1/4 E 1/2 SE 1/4 Sections can be further subdivided

12 12 Use the statements below to help you understand the Public Land Survey System. 1. Townships are numbered North and South of the Base Line and are labeled along the right and left margins of the map. 2. Ranges are numbered East and West of the Willamette Meridian in Oregon and are labeled along the top and bottom of the map. 3. Each township is 6 miles square and divided into 36 Sections. Note that the section numbers begin in the upper right had corner of the township and end at the lower right hand corner of the township. 4. Each Section is 1 mile square. 5. A section contains 640 acres which can be subdivided into smaller tracts. 6. A section can also be subdivided into sixteen 40 acre tracts which can be designated by compass directions. 7. A legal description of this parcel of 40 acres (Lot #2 previous page) would read: SE 1/4, SW 1/4, Section 14, T2S, R3W Note: Begin the legal description with the smallest designation. Our tour has ended. Good luck with your watershed explorations. Happy touring!

13 13 Glossary Contour Contour Interval Declination Hachure Isogonic Chart Latitude Longitude Map Map, Topographic Meridian Orientation Imaginary line on the ground, all points of which are the same elevation above or below a specific datum. A datum is a reference point used in surveying. Difference in elevation between two adjacent contours Angular difference between magnetic north and true (geographic) north at the point of observation; it is not constant but varies with time because of the wandering of the magnetic north pole. Any series of lines used on a map to indicate the general direction and steepness of slopes. These lines are often used to denote a depression (hole) in the land. Chart showing isogonic lines properly labeled with their magnetic declination. Angular distance in degrees, minutes, and seconds, of a point north or south of the equator. Angular distance in degrees, minutes, and seconds, of a point east or west of the Greenwich meridian. Any concrete or abstract representation of the distributions of features that occur on or near the surface of the earth or other celestial bodies. Map that presents the horizontal and vertical positions of the features represented. Great circle of the surface of the earth passing through the geographical poles and any given point on the earth s surface. All points on a given meridian have the same longitude. Establishing the correct relationship in direction with reference to points of the compass; the state of being in correct relationship in direction with reference to the points of the compass.

14 Prime Meridian Public Land System Quadrangle Relief Scale Section Township 14 Meridian of longitude 0 degrees, used as the origin of measure ments of longitude. The meridian of Greenwich, England, is the internationally accepted prime meridian on most charts. Public lands are subdivided by a rectangular system of surveys established and regulated by the Bureau of Land Management. The standard format for subdivision is by townships measuring 6 miles (480 chains) on a side. Townships are further subdivided into 36 numbered sections of 1 square mile (640 acres) each. Four- sided area, bounded by parallels of latitude and meridians of longitude used as an area unit in mapping. Elevations and depressions of the land or sea bottom. Relationship existing between a distance on a map, chart, or photograph and the corresponding distance on the Earth. One thirty-sixth of a township. A six square mile segment of land, the basic unit of the Public Land System Survey.

15 Questions: What is the name of your quadrangle map? Where do you find this information on your map? Answers will vary. The name of the map is found in the upper right corner and in the lower right corner. Both of these locations are outside of the map s boundaries. 2. How are quadrangle maps named? Quadrangle maps are named for some prominent feature within the area of the map. 3. or meridian lines run north and south and are measured in degrees east and west around the earth from Greenwich, England. Longitude 4. or parallel lines run east and west and are measured in degrees north and south from the equator to the poles. Latitude 5. Why are longitude lines more variable in length than latitude lines? Because longitude lines converge at the poles, the arc of their distance varies with the distance from the equator. 6. What does it mean when we say that a topographic map is a 7 1/2 minute map? A 7 1/2 minute map represents an area bounded by 7 1/2 minutes of latitude (one-eighth of a degree) and 7 1/2 minutes of longitude (one-eighth of a degree). 7. Which map shows the most detail a 7 1/2 minute or a 15 minute map? A 7 1/2 minute map shows more detail even though it covers less surface area than a 15 minute map. 8. If a location is just outside the boundaries of your topographic map, how would you find out the next map to use? Use the adjacent quadrangle map key located at the bottom of the map or look at the adjoining map s name listed in parenthesis along the sides or top and bottom of older quadrangle maps. 9. When was your map produced? If it was revised, when did this occur? Answers will vary. 10. What is the scale of your topographic map? What does this mean? Most topographic maps are at a scale of 1:24,000 which means that for every 1 unit of measurement on the map, the equivalent distance on land is 24,000 times that amount one inch to 24,000 inches, or 1 meter to 24,000 meters, etc. 11. What is a contour line? A contour line is a line that connects map points at the same elevation above sea level.

16 What is an index contour? An index contour is a heavier line that occurs at every fifth contour line. 13. What is contour interval? The contour interval is the vertical distance between two contour lines for example, 20 feet, 40 feet, or 80 feet. 14. What is the contour interval of your map? Answers will vary. Some maps may have more than one contour interval, for example, 20 feet in areas of high relief and 40 feet in areas of low relief. 15. What is indicated about the topography if the contour lines are very close together on a map? The landform in that area is very steep. 16. How do you know which direction a stream is flowing? When contour lines cross a stream, they form a v that points upstream. 17. What is the difference between magnetic north and true north? Which should you use to find the most accurate direction? Magnetic north is the compass direction influenced by the earth s magnetic core. It is not fixed and varies somewhat over time. True north or geographic north is the fixed point of the earth as it spins on its axis. Use true north as the most accurate direction. 18. Where do you find the declination distance on your map so you can adjust your compass to the most accurate direction? Declination information is usually located in the bottom left hand corner of the map. 19. What are the latitude and longitude coordinates in the top left corner of your map? Answers will vary. 20. What are the Universal Transverse Mercator (UTM) tick mark designations in the upper left hand corner of your map? Answers will vary. 21. What is the total distance in miles from the top to the bottom of your map at 45 latitude? What is the total distance in miles from side to side on your map at the same latitude? 8.63 miles from top to bottom and 6.12 miles from side to side. 22. What is the Willamette Meridian? Why is it important? The Willamette Meridian is the degree of longitude that runs through the Willamette Stone in the West Hills of Portland, Oregon. All of Oregon s range and township lines are measured from this point.

17 23. Describe the relationship of townships, ranges, and sections in the Public Land Survey System? All ranges are measured east or west of the Willamette Meridian. All townships are measured north and south of the Willamette Stone base line. Each township is 6 miles square and contains 36 sections. Each section is one mile square and consists of 640 acres. 24. What is the legal description at the mouth of the main stream closest to your community? Answers will vary, but should begin with the smallest designation (quarter section first) and end with township and range designations (i.e. SE 1/4. SW 1/4 Section 14, T2S, R3W). 17 Going Further 1. Design a set of questions (with an answer key) that could be asked with regards to your local topographic map. Design your questions so that the person answering the questions will have a better understanding of your watershed. 2. A landfill is planned for a site within the boundaries of your local topographic map. As a consultant for the city, give evidence that would support your choice for the placement of that landfill.

18 BIBLIOGRAPHY 18 Boyington, Marcy, Burgh, Dana Van. How To Teach With Topographic Maps. NSTA Special Publication. Arlington, Virginia (1994) Campbell, John. Map Use and Analysis.McGraw Hill. Boston, Massachusetts. (1998) Ferguson, Michael. GPS Land Navigation. GlassfordPublishing. Boise, Idaho.(1997) Haslam, Andrew. Make It Work! MAPS. World Book.Chicago, Illinois. (1996) Seidman, David. The Essential Wilderness Navigator. Ragged Mountain Press. Camden, Maine (1995) Silva. Teaching Orienteering. Johnson Worldwide Assc., Inc. Binghamton, NewYork (1991) Tasa Graphics. Introduction to Topographic Maps. Tasa Graphic Arts, Inc. CD. (1994)