General Geology/Topographic Maps

    Topographic Maps Objectives • Locate places using latitude and longitude and the PLS coordinate system • Read a topographic map • Determine elevations and slope angles using contour lines Laboratory Materials Needed • Madison East Topographic map quadrangle • Calculator Pre-lab Assignment Prior to lab, read the USGS Topographic Symbols handout (Appendix A), read the WI Public Land Survey System handout (Appendix A) and the information at the beginning of Exercise 1. Exercise 1: Introduction to Coordinate Systems Maps are useful because they provide a way to determine specific locations that can be shared with other people for many reasons, including personal, scientific and legal purposes. The two most commonly used coordinate systems for determining location are: 1) latitude and longitude, and 2) the Public Land Survey (PLS). Latitude and Longitude Latitude and longitude are used to determine precise point locations on the Earth’s surface. Lines of latitude specify the distance north or south of the equator, from 0o at the equator to 90o at the poles. Lines of latitude are also called parallels of latitude because they are parallel to the equator and to each other. Each degree of latitude is subdivided into 60 minutes of arc (1o = 60') and each minute is further subdivided into 60 seconds (1' = 60"). Latitude is always recorded with a hemispheric designation (N or S); for example Los Angeles is 33°42' N. Lines of longitude, or meridians, refer to the angular distance on the Earth measured from the prime meridian (0o), which runs through Greenwich, England, east or west through 180o. Degrees of longitude are also given in degrees, minutes or seconds, and are recorded with a hemispheric designation (W or E); for example Los Angeles is 118o 15' W. Topographic and bathymetric maps are bounded by parallels of latitude on the north and south edges, and meridians of longitude on the east and west edges. The latitudes and longitudes covered by the maps are printed at the four corners of the map in degrees (), minutes (‘) and seconds (“). Maps that cover 15 minutes of latitude and 15 minutes of longitude are called 15-minute series maps. A 7½ -minute series map covers 7½ minutes of longitude and 7½ minutes of latitude. Public Land Survey Latitude and longitude coordinates can be cumbersome to use when trying to subdivide land on a local scale. The Public Land Survey system provides a precise method for identifying the location of land in most states by establishing a grid system that systematically subdivides the land area into smaller and smaller areas(see PLS System Handout, Appendix A). The system involves establishing an initial point from which all locations of a state or region can be referenced. The initial point is defined by the intersection of a line of latitude (called the baseline) and a line of longitude (called the principal meridian). From the initial reference point, grid lines are surveyed at 6-mile intervals. The east-west lines surveyed at six-mile intervals define strips of land called townships. Each township is numbered north and south of the baseline. The first strip north of the baseline is designated Township One North (T1N), the second T2N, the third T3N, and so forth. The north-south lines surveyed at six-mile intervals east and west of the principal meridian define strips of land called ranges. Each range is numbered east or west of the principal meridian. The first strip east of the principal meridian is designated Range One East (R1E), the second R2E, the third R3E, and so forth. In Wisconsin the baseline coincides with and defines the Wisconsin-Illinois border, so that all townships in Wisconsin are North of the baseline. The principal meridian in Wisconsin is 90W longitude. Each square (formed by the grid) defines an area that is 36 square miles, which is also referred to as a township. Townships are further subdivided into 36 sections. Each section is one square mile in area. The sections are numbered as shown in Figure 3 of the WI Public Land Survey System handout (Appendix A). The section is listed before the township and range in the naming system ex. Sec. 11, T3S, R2W. Sections can be further subdivided into quarters and eighths, and even quarters of quarters. For example, the northeast one-quarter of the northwest one-quarter of section 11, township 3 south, range 2 west (or NE1/4, NW1/4, Sec. 11, T3S, R2W). Note that by convention, the smallest subdivision is always given first in the description and the township number always precedes the range number.         1. Use the information in the table below to answer the following questions. City Latitude Longitude Hana Bay, HI 20o45'N 155o59'W Los Angeles, CA 33o42'N 118o15'W Madison, WI 43o05'N 89o24'W New York, NY 40o38'N 73o50'W San Francisco, CA 37o19'N 122o25'W Seattle, WA 47o36'N 122o20'W a. Which city is farthest south? b. Is Los Angeles east or west of San Francisco?   c. How much farther north is Madison from Hana Bay, HI? If you are unsure how to subtract/borrow in a degrees, minutes, seconds situation please call your instructor over.       2. Use the PLS system to label the townships and ranges of locations A, B, C and D in the below. Record your answers in the space below the figure. Location A has been done for you. A: T5N, R3W B: C: D: 3. Now, use the PLS system to label the Section Locations of A, B, C and D in the below. Record your answers in the space to the right of the figure. Location A has been done for you.     A: Section 4 B: C: D: 4. Finally, label the Quarter Locations of A, B, C and D in the below. Record your answers in the space to the right of the figure. Location A has been done for you.   A: NE1/4 of the SW 1/4 B: C: D: 5. Identify locations E and F in the figures below by placing the appropriate letter (E and F) in the proper places in figure A through C. E. NW ¼, SW ¼, Sec. 17, T4N, R2E F. SW ¼, NE ¼, Sec 28, T5S, R4W   Exercise 2: Topographic Maps Topographic maps show the shape of the land. They are two-dimensional representations of the three-dimensional surface of the earth. These maps show to scale the width, length, and variable height of the land above a datum or reference plane (usually sea level). These types of maps are an indispensable tool to earth scientists in determining locations, landform types, elevations and other geological data. The United States Geological Survey has produced topographic maps since the late 1800’s. Today most of the United States has been accurately portrayed on these commercially available maps, which are sometimes called quadrangles. Over the years a systematic format has been developed to facilitate their use. Each map contains standard information about where the map is located, when the mapping has been updated or revised, scale, north arrows, and all maps use a standardized scheme of colors and symbols. Part A: General Map Information You will be provided a copy of a 7½ minute quadrangle map of the east side of Madison. Do not write or mark on the map. Every topographic map contains a variety of useful information along the borders of the map. Locate and use this information to answer the following questions. 6. Topographic maps are assigned a name for reference purposes. This name is usually located in the upper right corner of the map. What is the name of your map?   7. Look for a small reference map and compass arrow. Where on the map are these features located?   8. The names of adjoining quadrangle maps are given along the four sides and the four corners of the map. What is the name of the map that adjoins the north side of your map?   9. What is the name of the map that adjoins the east side of your map? Part B: Maps and Color Symbols Every symbol and color on a USGS topographic quadrangle map has a specific meaning. Refer to the USGS map or handout for a key of the symbols. Using the standard map symbols as a guide, locate examples of various types of roads, buildings, vegetation, and bodies of water on your map. 10. What colors are used for the following types of features? Feature Color and/or Symbol A Primary Highway B Unimproved Road C Buildings D Wooded Areas E Water Features Part C: Map Scales Since topographic maps are intended to be an accurate scale model of an area of the Earth’s surface, the features shown on the map will differ from those in the real world in size, but not in shape. The scale of a map is the ratio between the distance represented on the map and the actual distance on the earth's surface. Without a scale it would be impossible to translate a distance on a map to its corresponding distance in the real world. Three types of scales are commonly used on topographic maps: Graphic Scale - In this type of scale, a bar or line is marked off into lengths which correspond to some set interval of distance represented on the map. This scale may be the easiest to use, but it is not very precise. Precision is limited by the width of the inked lines on the scale. In a sense this type of scale is a ruler that can be used for measuring distance. Fractional Scale - This scale is very useful because it permits any degree of precision desired and allows the use of any type of unit of measurement. This scale presents the map and ground distances as a ratio. For example, a map may indicate a fractional scale of "1:5000". This means that one unit of distance (e.g. inches, centimeters, etc.) represents 5000 of those same units in actual distance. In other words the map is exactly 1/5000th as large as the real world. Note that the "1" always refers to the map scale and the larger number always refers to the equivalent ground distance in the same units measured on the map. Verbal Scale - This scale is a simply worded statement of the relationship between the map distance and the ground distance (e.g. 1 inch equals 1 mile). This type of scale is less common on USGS quadrangles, but is the most common scale on most highway maps. The USGS publishes maps on a variety of scales to meet the need for both broad coverage and local detail. Maps with small fractional scales (fractions with large numbers in the denominator, such as 1/250,000) cover large areas. Those with large fractional scales (fractions with smaller numbers in the denominator, such as 1/1000) cover small areas. 11. What is the fractional scale of your map?   12. Does your map have a graphical scale? If so, what does it look like?   13. Does your map have a verbal scale? If so, what does it say?   14. Depending on the map scale, one inch on a topographic map represents various distances on Earth. Remember 12 inches = 1 foot, 1 mile = 5280 feet. Convert the following scales to the units on the right. Scale 1 Inch on the Map Represents 1:24000 ____________ feet on earth 1:63360 ____________ miles on Earth 1:250,000 ____________ miles on Earth     Part D: Location Both coordinate systems (latitude/longitude and PLS) are used in determining locations on USGS topographic maps. Latitude and longitude are recorded in black on the sides (top, bottom, left and right) of the map. 15. What is the latitude of the north edge of the map?   16. What is the latitude of the south edge of the map?   17. How many minutes of latitude are there between the southern and northern edges of your map?   18. What is the longitude of the east edge of the map?   19. What is the longitude of the west edge of the map?   20. How many minutes of longitude are there between the eastern and western edges of the map?   21. What type of minute series is your topographic map? (select one) _________ 7.5 minute quadrangle _________ 15 minute quadrangle On a topographic map, the townships and ranges covered by the map are printed in red along the outer margins of the map. Section numbers are outlined on the map and their numbers are also printed in the centers of each section in red. 22. To reach the principal meridian that was used as a reference for this map, would residents of Madison have to travel east or west? (select one) _________ East _________ West 23. To reach the baseline they would have to travel north or south? (select one) _________ North _________ South 24. In what section, township and range is each of the following locations on the map? There may be more than one of each of these that satisfies the location. a. Yahara Hills Golf Course: b. Upper Mud Lake: c. The intersection of highway 151 and Ingersoll Street: Part E: Contour lines Topographic maps use contour lines to provide information regarding elevation. Contour lines are lines of constant elevation, i.e. it is a line that connects all points that have the same elevation above some reference plane. For most topographic maps, the reference or datum plane is mean sea level. The actual datum plane used on a topographic map is usually indicated in the lower, central margin of the map, just below the map scale with the phrase “Datum is …” The rules for constructing contour lines are: Every point on a contour line is at the same elevation. Contour lines never cross, divide or split. A contour line always closes upon itself, and, therefore, always encloses areas of greater elevation. All points outside of the curve represent lower elevations than that of the topographic contour line. Therefore hills are represented by a concentric series of closed contour lines. Contour lines will always form a V-shape pattern whenever they cross a valley or a deep canyon with the apex or point of the 'V' pointing uphill. Close spacing between contours indicates a steep slope, whereas widely spaced contours represent a gentle slope or a relatively flat area. The contour lines are constructed at regular intervals of elevation or at a uniform contour interval. The contour interval is defined as the vertical distance between any two adjacent contour lines. The contour lines are then constructed at whole number multiples of the contour interval from some base level (or datum plane). In most cases the base level is mean sea level. The contour interval is usually indicated in the lower central margin of the map with the phrase “Contour interval …” A concentric series of closed contours with hachure marks (“tick marks”) on the downhill side of the contour line represents a closed depression. Note that all rules applying to contour lines also hold for hachure lines (with the exception that hachure lines enclose areas of lower elevation) To help determine the elevation of the contour lines every fourth or fifth (depending on the contour interval) contour interval is printed with a bolder line and the elevation of the line is printed. Reference points for elevation, called bench marks (BM) are often present on the map (printed in black) and can be used to establish elevations. Spot elevations are not as accurate as benchmarks and are usually printed in brown. The elevation of any point on a map that is not on a contour line can only be approximated from the contour lines. For example, a point between the contours of 850 feet and 860 feet can only be described as being between those elevations. An approximation of the height is usually established by the proportional distance the point is between the two adjacent contour lines. Topographic maps include the bathymetry or depth of water bodies, including lakes and bays. Lines of bathymetry are printed in blue on the maps and can be used to determine the depth to the bottom of the water body. They should not be confused with the contour lines. The elevation of the surface of a water body is usually printed in blue in the center of the feature. Relief is a term used to describe the difference in elevation between the highest and lowest points in an area. Simply subtract the lower elevation from the higher elevation to determine the local relief between two points. Total relief is used to describe the difference between the highest and lowest elevations on a map. Figure 2 shows both a perspective view and a contour map of a hypothetical area situated along a coastline. The elevations of several contour lines are measured in feet and are identified on the map. Datum for the map is mean sea level. Use Figure 2 to answer the following questions: 25. What is the contour interval used in Figure 2?   26. Indicate on the map in Figure 2 two areas that have the steepest slopes by writing the word “steep” on the map. 27. Notice what happens when the contour lines cross a stream. The “peak” or “V” formed by the contour line as it crosses a stream points in which direction (select one): _________ upstream or _________ downstream 28. What are the elevations of the points designated as A, B, and C? A = ____________ B = ____________ C = ____________ 29. What is the total relief shown on the map? Show your calculation.   30. What is the slope of the mountain located on the east side of the diagram from its summit directly south to the ocean in feet per mile? Show your calculation. Remember: slope = rise / run   Figure 2 – Hypothetical perspective view and a contour map of an area situated along a coastline. Elevations measured in feet. (Source USGS)   Now look at the quadrangle map that was provided in the lab, and answer the following questions. 31. What is the datum that has been used for determining the elevations on the map? This information will be printed within the legend information.   32. What is the contour interval of the map?   33. What is the highest elevation on the map? You will need to search the map for this elevation. HINT: It is a surveyed location. Look for a small triangle (Δ) with the elevation written next to it in black.   34. What is the lowest elevation on the map? You will need to search the map for this.   35. What is the total relief of this map? Show your calculation.   36. What artificial structure is located in the NW ¼ NE ¼, Section 23, T7N, R10E?   37. What feature is located in the SW ¼ NW ¼ Section 34, T8N, R10E?   38. What is the elevation of the hill located in the SE ¼ , SE ¼ Section 12 T6N, R9E?