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|Essential Question: |

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| |Chapter 3: Modeling The Planet |

| |Map: |

| |A Map is a flat, two dimensional model or representation of the Earth’s surface. |

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| |Map Projection: |

| |Modeling a round Earth on a flat surface produces disjtortion. For example, a projection that accurately represents the |

| |shapes of the continents will distort their size (example: Greenland). |

| |Cartographers have developed different map projections to reduce distortion to different areas for different purposes. |

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| |Projection: |

| |A projection is a mathematical means of transferring information from the Earth's three-dimensional curved surface to a |

| |two-dimensional map. |

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| |Mercator Projection: |

| |Strengths: |

| |-shows the entire world |

| |-shows direction as a straight line which makes it good for navigation |

| |-true shape and distances within 15 degrees of the equator |

| |Weakness: |

| |-great distortion of area and shape at high latitudes |

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| |Gnomonic Projection: |

| |Strengths: |

| |-shows the shortest distance between two points |

| |-true shape and distance at the poles |

| |Weakness: |

| |-great distortion of area and shape as you move away from the center point (the lower the degree the greater the |

| |distortion) |

| |-does not show the entire world on one map |

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| |Polyconic Projection: |

| |Strengths: |

| |-shows true shape and size of land masses relative to other land masses at Mid-Latitudes |

| |Weakness: |

| |-great distortion of area and shape as you move away from the Mid-Latitudes |

| |-does not show the entire world on one map |

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| |Map Scale |

| |Map scale expresses the relationship between the distance on a map and the true, corresponding distance of the same area|

| |of the Earth’s surface. |

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| |This comparison is usually shown as a ratio or fraction and is called a fractional Scale. |

| |On Topographic Maps, both sides of the ratio represent the same units. |

| |For example, 1:12,000 means that one centimeter of distance on the map is equal to 12,000 centimeters on the ground. |

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| |A Bar Scale, or map ruler, is a line drawn on a map of known ground length. |

| |Bar Scales are useful because they allow the map reader to quickly estimate distance by laying a piece of paper next to |

| |the scale, marking the paper, and then using the paper like a ruler to measure map distance. |

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| |Map Orientation |

| |Orientation is using the cardinal directions of North, South, East and West on the map and determining the same |

| |directions on the ground. |

| |A compass is usually used to determine the cardinal directions on the ground. |

| |A compass does not normally point to true north. Only in a few places does magnetic North and geographic North line up|

| |with each other. |

| |The direction in which the compass needle points is referred to as magnetic north, and the angle between magnetic north |

| |and the true (geographical) north direction is called Magnetic declination. |

| |Effects of Magnetic Declination: |

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| |Declination or Degrees off course |

| |Error off target after 10 miles |

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| |1o |

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| |920 feet (280 meters) |

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| |1o |

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| |4,600 feet (1,402 meters) |

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| |1o |

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| |9,120 feet (2,795 meters) |

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| |Topographic Maps |

| |A topographic Map is the representation on a flat surface of part of the Earth’s surface drawn to scale. |

| |Topographic maps show distance relationships and elevation, and help visualize Topography, or the way the land actually |

| |looks in three dimensions. Topography actually means “the shape, elevation, and slope of the land”. |

| |On topographic maps different symbols and colors are used to indicate different features including bodies of water and |

| |human-made structures. |

| |The color blue indicates features associated with water. |

| |The color green indicates features associated with vegetation. |

| |The color brown indicates elevation. |

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| |Contour Lines |

| |The distinctive characteristic of a Topographic Map is that the shape of the Earth's surface is shown by contour lines. |

| |They are always shown as brown lines on a topographic map. |

| |Contour Lines are imaginary lines that join points of equal elevation on the surface of the land above and below a |

| |reference point, such as sea level. |

| |Every point on a contour line, therefore, has the exact same elevation. |

| |Contours make it possible to determine the shape of the land, measure the height of mountains, depths of the ocean |

| |bottom, and steepness of slopes. |

| |Depending on the degree of elevation change that occurs in a given area, a topographic map can have few or many many on |

| |it. |

| |The greater the elevation change, the more contour lines there will be on a map. |

| |Contour lines can be drawn for any elevation, but to prevent a map from becoming “cluttered”, only certain elevations |

| |are drawn. |

| |These elevations are chosen to be evenly spaced vertically. |

| |This spacing is referred to a Contour interval, which we will discuss later. |

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| |There are several different types of contour lines on topographic maps. They are index Contours, intermediate Contours |

| |and depression Contours. |

| |Contour Lines that have elevations shown are called index Contour Lines. |

| |These types of contour lines tend to be displayed on every 100 meter or foot contour line. |

| |They are darker than others. |

| |Contour lines that are draw between Index contour lines are referred to as intermediate Contour Lines |

| |They do not have their elevations shown. |

| |depression Contours are contour lines that show areas that are surrounded on all sides by higher elevations. Depression |

| |Contours have perpendicular hash marks on them. And are often circular in shape. |

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| |Contour Lines make it possible to determine the shape of the land without looking being at the location depicted on the |

| |map. Using the following Rules make it helpful in understanding the information Contour lines can tell us about an |

| |area. |

| |Rules of Contour Lines |

| |1. All points on a contour line are at the same elevation. |

| |2. Contour lines are drawn at uniform vertical intervals, called the contour interval. |

| |3. Contour lines do not cross, except at overhangs, which are rarely mapped. Contour lines may meet only at a vertical |

| |cliff. |

| |4. The spacing of contour lines indicates the degree and kind of slope: |

| |closer spacing = steeper |

| |wide spacing = gentler |

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| |5. U-shaped or V-shaped lines indicate valleys or ridges. Contours crossing a river or gully form a V or U whose apex |

| |points uphill. Contours crossing a ridge form a V or U which points down the ridge. |

| |6. Closed contour lines (circles or ellipses) indicate peaks. |

| |Exception: depressions also have closed contour lines, but these lines have hash marks on them and are at the same |

| |elevation as the closest non-hachured contour. |

| |7. Spot elevations (or bench marks, B.M.) may be marked on the map with an exact altitude. Mountain summits are very |

| |often marked in this way. |

| |8. The difference in elevation between the highest and lowest point of a given area is the 'maximum relief' of that |

| |area. |

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| |Contour Interval |

| |Contour Interval is the difference in elevation between adjacent contour lines. |

| |Contour interval for a map is found in the legend or in the margin. |

| |The contour interval is different for each map. |

| |In areas with a large elevation increase, contour interval is usually larger to prevent the map from becoming cluttered |

| |with too many contour lines. |

| |There are times you will be required to identify the contour interval map sections that do not show the information |

| |usually found in the map margin. (Usually when only a portion of a map is shown or the margin of the maps has been |

| |removed) |

| |This is accomplished by: |

| |Finding the elevations of two different Index Contours. |

| |Determining the total elevation change between the two Index Contours |

| |Dividing the total elevation change between the two Index Contours by the number of contour lines from one Index Contour|

| |to the next Index contour. |

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| |Slope and Elevation |

| |Topographic maps are not just used for determining elevation. They can also be used to help visualize topography. |

| |One of the most basic visualizations is Slope or Gradient. |

| |Slope or Gradient refers to the change in elevation over a certain distance (rise over run). |

| |On a map, this is shown as the distance between one contour line and the next. |

| |High (steep) gradient or slope occurs where there is a large change in elevation over a short distance, and low (or |

| |gentle) gradients occur in areas where there is little change in elevation over a given distance (the land is “flat”). |

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|Summary: |

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|Essential Question: |

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| |How to determine Slope or Gradient: |

| |You need to determine the change in elevation that occurs between those two points (example: if you start at 1400 feet |

| |in elevation and the end of your measurement is at 3165 feet, your elevation change is 1765 feet). |

| |Then you need to determine the distance between two points (example: 2 mile). |

| |Then you divide the change in elevation by the distance. (Slope = Rise/Run). |

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| |Topographic Map Profiles |

| |Topographic map profile allows you a visual side perspective of an area so that you can see the land forms from a side |

| |view. Similar to what you would see if you were standing on the ground in that area. |

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| |Profiles are created using the following steps: |

| |Draw a line between two points on a map |

| |Using a piece of paper transfer the elevation readings (corresponding to the contour lines drawn on the map) on to the |

| |paper |

| |Then using a vertical graph paper transfer the elevation data on to the graph paper. |

| |Connect the elevations to show the profile of area along the line you drew on the map. |

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