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EARTH AND SPACE SCIENCE
Chapter 3 Models of the Earth
3.2 Mapping Earth’s Surface
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3.2 Mapping Earth’s Surface Objectives
• Explain two ways that scientists get data to make maps.
• Describe the characteristics and uses of three types of map projections.
• Summarize how to use keys, legends, and scales to read maps.
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Introduction
• A globe can accurately represent locations, relative areas, and relative shapes of Earth’s surface features since the globe is spherical – like the Earth!
• The finer details of Earth’s surface cannot be accessed using a globe.
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How Scientists Make Maps
• Cartography is the science of making maps.• Cartographers are scientists who make maps.• Cartographers use data from a variety of
sources in order to make maps.– Field Survey – cartographer walks or drives through
an area and takes measurements to be plotted on a map
– Remote Sensing – images of the Earth taken from a plane or satellite are used to make maps
– Combination of field surveys and remote sensing are often used to map an area
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Map Projections
• A map is a flat representation of Earth’s curved surface.
• Distortion in size, shape, distance, or direction may occur when transferring a curved surface area to a two dimensional map.
• The larger the area represented on the map, the greater the distortion tends to be.
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Map Projections
• A map projection is a flat map that represents the three-dimensional curved surface of Earth.
• Though no projection is entirely accurate, some types of projection maps are more useful to us than others.
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Map Projections
• Cylindrical (Mercator) projections are constructed with straight meridians and appear as if someone put a lighted globe in the middle of a paper cylinder with the paper only touching at the equator.
• This map is accurate at the equator, but distorts size and distances near the poles.
• Locating positions is easier on this type of map because of the grid created by making the meridians parallel.
• The mapping of small areas is done this way because distortion of those areas is minimal.
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Map Projections
• Azimuthal (Gnomonic) projections are made by putting a sheet of paper against a transparent lighted globe such that the paper touches the globe at only one point.
• Very little distortion occurs at the point of contact on this type of map, yet the distortion increases as you move away from the point of contact.
• Azimuthal projections show unequal spacing between parallels which results in distortion of distances and directions.
• Azimuthal projections are useful for navigators to plot routes for air travel because drawing a straight line on an azimuthal projection is the shortest distance between two points on a globe.
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Map Projections
• A conic projection is made by placing a paper cone over a lighted globe so that the axis of the cone aligns with the axis of the globe.
• The cone touches the globe at one parallel of latitude.
• Distortion is minimal at the point where the cone touches the latitude of the globe.
• Polyconic projections, a series of conic projections used to make a map, are used to minimize distortion.
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Reading a Map
• In order to read a map, one must be able to understand symbols and figure direction and distance.
• Most maps are made so that north is at the top, east to the right, west to the left, and south to the bottom.
• Lines of longitude are often parallel as well as lines of latitude being parallel.
• A compass rose often is used to determine direction on the map.
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Reading a Map
• Maps with multiple symbols will often have a legend – an explanation for what the symbols mean.
• The scale of a map shows the relationship between the distance on the map and the actual distance.– Graphical scale – marked line similar to a ruler that
will be of a specified distance– Fractional (ratio) scale – mathematic representation
of the relationship, often a ratio of map distance to actual distance
– Verbal scale – verbal expression of the distance relationship between the map and actual area
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References
• Globe - http://www.library.yale.edu/MapColl/globes.html
• Topographic Map - http://www.adirondacknorthway.net/mappages/mount_marcytopo.php
• Cylindrical Projection Map - http://www.3dsoftware.com/Cartography/USGS/MapProjections/Cylindrical/MillerCylindrical
• Cylindrical Projection - http://www.cnr.colostate.edu/class_info/nr502/lg1/map_projections/form_case_aspect.html
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References
• Azimuthal Projection - http://www.cnr.colostate.edu/class_info/nr502/lg1/map_projections/form_case_aspect.html
• Azimuthal Projection Polar Map - http://www.3dsoftware.com/Cartography/USGS/MapProjections/Azimuthal/Gnomonic
• Polyconic Projections - http://www.nationalatlas.gov/articles/mapping/a_projections.html
• Conic Projection - http://www.yourdictionary.com/ahd/c/c0570900.html
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References
• Compass Rose - http://cuip.uchicago.edu/~tjones/home/science/eq/page8.html
• Map Scale - http://cropsoil.psu.edu/Courses/Soils101/lectures/MapScale/MapScale05.html
• Map Legend - http://www.dot.state.oh.us/map1/ohiomap