EARTH AND SPACE SCIENCE Chapter 3 Models of the Earth 3.3 Types of Maps
3.3 Types of Maps Objectives • Explain how elevation and topography are shown on a map. • Describe three types of information shown on geologic maps. • Identify two uses of soil maps.
Introduction • Earth scientists use a variety of maps that show a number of characteristics of an area. • Types of rocks • Differences in air pressure • Depth of ground water • Maps can also be used to show elevation, locations, boarders, and other surface features.
Topographic Maps • Topographic maps show surface features (topography) of the Earth. • Natural features, such as rivers, valleys, and mountains, are shown on topographic maps. • Man-made structures such as roads, buildings, dams, and railroads may be shown on topographic maps. • Field-collected survey points and aerial photographs are often used in constructing topographic maps.
Topographic Maps • Elevation is height measured above mean sea level (average between high tide and low tide). • Topographic maps provide information about the size, shape, and elevation of surface features.
Topographic Maps • Contour lines are used on topographic maps to show elevation. • Each contour line is used to connect points that have the same elevation, therefore, they never cross. • Since all the contact points at a given elevation are connected, the shape of the contour lines reflects the shape of the land. • The contour interval is the difference in elevation between one contour line and the next.
Topographic Maps • The scale of the map and the contour of the land help the cartographer choose the contour interval. • Relief is the difference in the highest and the lowest point of the area being mapped. • Index contours, every fifth contour line, are bold and have the elevation written in them. • Exact elevations are marked with an “x” and are labeled.
Topographic Maps • Contour lines spaced widely apart indicate gradual change in elevation. • A steep slope or cliff would have many contour lines close together. • A contour line that forms a “V” indicates a valley. • If a stream runs through that valley, the “V” points upstream because water runs down hill. • A closed loop indicates a hilltop or mountain. • A depression is noted with a closed loop that has short lines perpendicular to the contour line on the down-hill side of the contour line.
Topographic Maps • Symbols are used to show certain features on topographic maps. • Water is generally shown in light blue. • Major highways and other roads are generally red. • Forested areas are usually green. • Other symbols often apply. • Refer to the legend for a complete list of symbols and color schemes.
Geologic Maps • Geologic maps are used to show the age and type of surface bedrock in a mapped area. • This information often reveals fault zones, astroblems, type of rock, and other features. • Geologic maps are created on top of base maps which are used to show roads and surface features to help locate and identify geologic units. • The base map is usually printed in a lighter color than the rest of a geologic map.
Geologic Maps • A geologic unit is a type of rock with a given age range and type. • Geologic units are distinguished by color. • Geologic units of similar age are usually assigned colors in the same family. • A set of letters is also assigned to each geologic unit. • The first letter (capital) symbolizes the rock’s age and the following letters (lower-case) symbolize the exact unit.
Geologic Maps • Contacts, places where two rock units meet, are shown on geologic maps. • There are two types of contacts. • Fault contacts are places where there was a break in the rock along which movement has occurred • Depositional contacts represent distinctly different depositional occurrences. • Strike indicates which directions the bed runs. • Dip indicates the angle at which beds tilt.
Soil Maps • Scientists construct soil maps to classify, map, and describe soils. • Soil surveys are most commonly preformed at the county level and provide data used in constructing soil maps. • The Natural Resources Conservation Service (NRCS), a branch of the United States Department of Agriculture (USDA), is in charge of compiling and managing soil data. • For more than a century, the NRCS has been mapping the distribution of soil in the United States.
Soil Maps • A soil survey consists of three parts. • Text – includes general information about the topography, geology, and climate of the area mapped • Maps – a general map shows the approximate location of soil types in the area and a second map shows detailed information about the soils in the area • Tables – display the data used to construct and describe the area detailed by the map • Land management and agriculture depend heavily on soil maps for information that will help farmers, developers, and civil engineers determine the best possible use of soil resources in the given area.
Other Types of Maps • Scientists used maps for a variety of purposes that may include tracking groundwater flow or lightning strikes. • Data are plotted from various points around the study area and then isograms are used to connect points of identical data. • Maps are used in every branch of Earth Science from a meteorologist tracking a storm to a hydrologist tracking groundwater flow to predict where water shortages will occur.
References • Hawaii Topographic Map - http://www.mste.uiuc.edu/courses/ci407su01/students/south/magrini/finalproject/overlaymap.html • Index Contour Lines - http://www.therockerbox.com/how_to_use_a_map_4.htm • Contour Depression - http://www.westseneca.wnyric.org/West_Seneca_Web_Pages/east%20senior/teacher/Chris%20Hart/Home/labs/vocab/making_a_contour_map/making_a_contour_map_voc.htm • Contour Cross Section - http://interactive2.usgs.gov/learningweb/textonly/teachers/mapsshow_act4.htm
References • Geologic Map of Alabama - http://www.geo.ua.edu/documentation/geology1.html • Soil Map of Florida - http://grunwald.ifas.ufl.edu/Projects/NRC_2001/NRC.htm