Isolines

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Isolines

• An isoline is a line connecting points of equal
  value.

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Examples of isolines

• Isotherms
• points of equal temperature
• Isobar
• points of equal barometric (air) pressure
• Contour
• points of equal altitude
• Concentration of chemicals
• Anything else you can get a value for.
• (The weather channel loves isolines!)

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Rules for Drawing Isolines

• 1. Isolines connect points of equal value.

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• 2. Isolines are gentle, curving lines- no sharp
  corners.

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• 3. Isolines are always closed curves even though
  the map might only show part of it.

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• 4. Isolines NEVER cross- this would mean that one
  point has two different values. Ex one spot has
  two temperatures?

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• 5. Isolines usually are parallel. (They have a
  parallel trend.)

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?Practice Drawing Isolines 10 unit interval
95 91 85 81 80 76 75 75 76 74
79 80 82 92 84 79 77 77 76 75
77 76 75 77 79 82 89 75 68 65
66 67 63 64 65 71 75 78 81 75
72 65 58 56 49 55 61 63 66 72
75 75 79 77 77 66 51 49 47 58
63 65 67 69 67 80 77 73 61 55
47 44 55 57 59 65 64 66 81 80
78 76 62 61 59 58 57 58 59 62
65 82 83 80 78 77 72 67 63 62
60 58 62 64
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?Practice Drawing Isolines 10 unit interval
95 91 85 81 80 76 75 75 76 74
79 80 82 92 84 79 77 77 76 75
77 76 75 77 79 82 89 75 68 65
66 67 63 64 65 71 75 78 81 75
72 65 58 56 49 55 61 63 66 72
75 75 79 77 77 66 51 49 47 58
63 65 67 69 67 80 77 73 61 55
47 44 55 57 59 65 64 66 81 80
78 76 62 61 59 58 57 58 59 62
65 82 83 80 78 77 72 67 63 62
60 58 62 64
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Gradient

• Gradient shows how quickly the value changes from
  one point to another.

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• A steep (high) gradient changes quickly and the
  isolines are close together.
• A gentle (low) gradient changes slowly and the
  lines are far apart.

Steep area
Gentle area
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Gradient

• ?List three situations in which it would be
  useful to calculate gradient.

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Gradient Example
On a topographic map, the elevation at your house
is 480 m. A hill, 4 km away, has a height of 980
m. What is the gradient from your house to the
top of the hill?
980 m - 480 m
4 km
Gradient 125 m/km
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Gradient Example

• ? It is 7 degrees Celsius in Ithaca, and 25
  degrees Celsius in Miami. Miami is 2600km away
  from Ithaca. What is the temperature gradient
  from Ithaca to Miami?

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Gradient Example

• ? Low pressure system is centered over Syracuse
  with a barometric pressure of 1011 mb. The
  barometric pressure in Norwich, 36 miles away, is
  1019 mb. What is the pressure gradient?

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Gradient Example

• ? A ball rolls down a 1.5 meter plank in 2.7
  seconds. The top of the plank is .7 m above the
  ground. What is the gradient of the plank?