Lab 6 Topo Maps-1

GEO 201 Physical Geology Name____Grace Heassler_____ Lab 6 - Topographic Maps (25 points) Introduction Topography means “the shape of the land”. In this lab you will become familiar with topographic maps. Topographic maps illustrate scale, width, length and height of landforms. Topographic maps are an important tool for anyone studying the earth. We will use some of the skills gained in this lab, such as drawing contours and profiles, in later labs. Learning Outcomes  Explain how contours are used to show elevation information and landforms on a map. (questions 1-3)  Understand and explain different types of map scale, such as fractional scale and bar scale. (questions 4-5)  Explain how latitude and longitude are used to describe location. (questions 6-8)  Draw and use contours to visualize spatial data (such as spot elevations). exercise 2)  Draw a topographic profile. (exercise 3)  Find the latitude and longitude of a location on a map. (questions 7, 19, 20)  Relate latitude/longitude to map areal coverage. (question 17)  Read elevation data and interpret contours on a topographic map.(questions 10, 11, 15, 18)  Calculate elevation change and gradient (slope) from topographic maps.(questions 12, 21)  Read distances on a map using a ruler and bar scale.(questions 13, 14, 16) Map Coordinate Systems A coordinate system allows us to describe the location of any point on the surface of the Earth. Lines of latitude (also known as parallels) are the horizontal lines that circle the globe. These lines are known as parallels because the run in the same direction as (are parallel to) the Equator . The Equator is the imaginary line located at 0° latitude and is halfway between the North Pole and the South Pole, which are 180° apart. This means the South Pole is 90° S and the North Pole is 90° N. Lines that run from the North Pole to the South Pole are lines of longitude (also known as meridians ). The line at 0° longitude is the prime meridian and runs through the Royal Observatory in Greenwich, England. Meridians are counted east and west from the prime meridian up to a maximum of 180° longitude at the International Date Line, on the opposite side of the world from the prime meridian. The north-south lines of longitude and the east-west lines of latitude form a grid on the Earth’s surface. The basic unit of latitude and longitude is the degree . The degree (°) is further subdivided into minutes and seconds . On topographic maps the latitude and longitude are expressed in degrees, minutes, and seconds. Each degree is divided into 60 minutes ( ' ). Each minute is divided into 60 seconds ( " ). If you are interested in a general location, then just use degrees. But for more precision, specify minutes and seconds. You will also see other numbers for different coordinate systems used on topographic maps: the values in feet are for state plane coordinates, and the unitless numbers in bold (with superscripts) are for UTM (Universal Transverse Mercator) coordinates. Map Series GEO 201 Physical Geology Page 1 of 10 Lab 6 Topographic Maps

The map series tells you the amount of latitude and longitude covered by a map and is listed in the upper right corner of the topographic map. Commonly encountered map series are 7.5 minute and 15 minute. A 7.5 minute series map covers an area that spans 7.5 minutes of latitude and 7.5 minutes longitude. Because there are 60 minutes in one degree, sixty-four 7.5 minute maps are needed to cover one full degree of latitude or longitude (8 per side). Map Scales A map represents a portion of the earth's surface. Since an accurate map portrays a condensed view of the land, each map has a scale that indicates the relationship between a certain distance on the map and the distance on the ground. The most common map scale used in the United States is the United States Geological Survey (USGS) 7.5 minute series quadrangle (“quad” for short) which uses a scale of 1:24,000. This is the map’s fractional scale . In fractional scale, the units do not matter as long as they are the same: 1:24,000 literally means 1 inch on the map equals 24,000 inches on the ground, 1 mile equals 24,000 miles, one meter equals 24,000 meters, etc. Because the fractional scale is a ratio, the units on the map cancel units on the ground as long as they are the same. Alternatively we can show the map’s scale visually using a graphical or bar scale , generally located at the bottom of the map. A graphic scale is simply a line marked with distance on the ground that the reader can use along with a ruler to distances on the map. Contour Lines Contour lines (or contours ) describe the elevation information on topographic maps. A contour line connects points of equal elevation. Contours are drawn on a map at a uniform vertical distance, known as the contour interval . Some contour lines are drawn in bold and are labeled with the elevation. These bold contours are called index contours . In between two index contours are intermediate contours. On standard USGS topographic maps with a contour interval of 40 feet, every fifth contour (200) feet is an index contour shown by a thicker line and labeled with its elevation. Contour lines are typically drawn in brown. Blue lines are used to represent rivers and streams, while double lines of various colors and thicknesses represent different types of roads. Political boundaries are shown in black, while the numbered squares represent one square mile sections in the U.S. land survey system. In the figure on the right, the thick lines (labeled 700 and 800) are index contours. The four contours in between the index contours are called intermediate contours. Using both the index and intermediate contours you can calculate the contour interval. The contour interval in this example is 20 feet because we cross five contours to go from one index contour to the other (100 ÷ 5 = 20). The arrangement, spacing, and shape of contours provide the map user an idea of what the actual topography of the land surface looks like. For example, closely spaced contours indicate a steep GEO 201 Physical Geology Page 2 of 10 Lab 6 Topographic Maps

slope while widely spaced contours depict a gentle slope. River valleys are shown with contour lines that “V” upstream. Below is a portion of the Spruce Knob quadrangle in West Virginia which illustrates how different topographic features appear on a topographic contour map. GEO 201 Physical Geology Page 3 of 10 Lab 6 Topographic Maps Low gradient (gentle slope) Widely spaced contours Circular contours indicate a hill. High gradient (steep slope) Closely space contours Contours “V” upstream