ESS 101 B Au Laboratory 1 : Geologic Techniques Exam Questions and Answers | Latest Updated 2026/2027 | Graded A+ | 100% Correct.

ESS 101 B Au Laboratory 1 : Geologic Techniques Exam Questions and Answers | Latest Updated 2026/2027 | Graded A+ | 100% Correct. Topographic Maps A topographic map is a three-dimensional representation of the Earth’s surface, where surface elevation or topography is represented by contour lines. Topographic maps are used in the earth sciences because they present a reduced view of the Earth’s surface and show the size, shape, and interrelationships of the natural landscape. Being able to use topographic maps is an invaluable tool for many different professions, as well as for recreational hiking. This lab will help acquaint you with the different components of topographic maps and their potential application to geologic problems. Figure 1-3: A composite satellite photograph of the United States at night . 3 Location Figure 1-4: World globe showing latitude and longitude coordinates4 . Latitude and Longitude Most maps have a geographic coordinate grid, which can be used to determine location. The most commonly used coordinate system is latitude and longitude. Latitude is an angular distance measured north or south of the Earth’s equator, which is 0° latitude. It varies from 0° to 90° north and from 0° to 90° south (Figure 1-4). Lines of latitude encircle the Earth parallel to the equator and are called parallels because they are parallel to one another. Lines of longitude represent the angular distance measured east or west from the prime meridian (0° longitude), which passes through the Royal Astronomical Observatory in Greenwich, England. Lines of longitude range from 0° to 180° east and from 0° to 180° west (Figure 1-4). The international date line is the line represented by both 180° east and 180° west longitude. Lines of longitude are termed meridians and encircle the Earth in a direction perpendicular to the equator. Meridians of longitude converge at the North and South poles; thus, they are neither parallel nor equally spaced except along a given line of latitude. Ground distance represented by a degree or minute of longitude decreases poleward from the equator because of this convergence. Units of latitude and longitude are expressed in degrees (°), and further subdivided into minutes (60 minutes ['] = one degree), and seconds (60 seconds [''] = one minute). For example, Seattle is located at 47°27'00'' N, 122°18'00'' W. To accurately convey a specific location on the Earth’s surface, it is important to state whether its latitude lies north or south of the equator and longitude lies east or west of the prime meridian. By convention, a location’s latitude is stated first, followed by its longitude coordinate. Scale Most maps represent a reduced image of a larger area. The amount of reduction is defined by a map’s scale and may be expressed in the following ways: (1) Graphic Scale: Scale is indicated by a calibrated bar or line. For example, the bar scale shown in Figure 1-5a represents a distance of two kilometers on the Earth’s surface. Figure 1-5a: Example of a graphic scale from a topographic map. (2) Fractional Scale: Scale is expressed as a fixed ratio between a distance measured on a map and an equal distance measured on the Earth’s surface. This ratio is termed the representative fraction. For example, a fractional scale of 1:24,000 indicates that one distance unit on the map (inches, feet, centimeters, etc.) equals 24,000 of the same distance units on the surface of the Earth (Figure 1-5b). Figure 1-5b: Example of a fractional scale from a topographic map. Magnetic Declination On the surface of the Earth the magnetic north pole (where a compass needle will point) is not the same location as the “true” or geographic north pole, which defines the earth’s axis of rotation. The angular distance between geographic and magnetic north at a given location represents its magnetic declination. Because magnetic declination varies over time and space, a symbol and explanation are provided on the lower margin of most U.S. Geological Survey (USGS) topographic maps (Figure 1-6). This symbol shows the magnetic declination for the center area of a topographic map at the time it was published or revised. Figure 1-6: USGS magnetic declination symbol. The star represents geographic north, GN is grid north, and MN is magnetic north. This symbol shows a magnetic declination of 16½°. Within the conterminous United States, magnetic declination varied between 20° west in Maine and 20° east in Washington in 1995 (Figure 1-7). Because the magnetic poles migrate over time, in 2018 the magnetic declination in Seattle was almost 16° east. Up to date magnetic declination measurements are needed to determine accurate directions when mapping and navigating over large distances. Geoscientists and backpackers alike require accurate magnetic declination data to set their compasses appropriately when using base maps. Figure 1-7: Magnetic declination map for the conterminous United States, 1995 (U.S. Geological Survey). Up to date declination data within the conterminous United States can be acquired using an online declination calculator found on the National Geophysical Data Center’s (NGDC) web site: Contour Lines Topographic maps are important tools used by earth scientists because they show the three-dimensional configuration of the Earth’s surface by means of contour lines, which connect points of equal elevation. Contour lines may be visualized as the intersection of a series of equally spaced, horizontal planes with the Earth’s surface. The relationship between a topographic map and the land surface it represents is illustrated in Figure 1-8.