isolines and contour lines
TRANSCRIPT
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Isolines and Contour Lines
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Isolines
• To map particular characteristics of an area, such as elevation, the amount of rainfall, or the temperature isolines are often used.
• An isoline is a line on a map that connects points of equal value.
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Isolines
• For example contour lines on topographic maps are isolines that show elevation.
• When we study weather and climate, we will use several kinds of isolines, such as isotherms, to show temperatures, and isobars to show atmospheric pressure
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Basic Rules of isolines
1. An isoline connects points on a map where the value of some phenomenon is the same.
2. Isolines are drawn at regular intervals.• For example every 5° of temperature difference.
3. Isolines are always closed lines, although the often close beyond the margins of a map.
4. Isoline NEVER cross each other.5. When isolines are close together, they show a rapid
horizontal change in the phenomenon; where they are far apart, the show a gradual horizontal change.
6. Values inside a closed isoline are either higher or lower than those outside the close isoline
• It is usually clear which is the case based on the pattern of adjacent isolines.
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Figure One
• This drawing will help illustrate how isotherms are drawn.
• Figure One shows a simple map with temperatures plotted for 17 different cities.
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http://www.ux1.eiu.edu/~cfjps/1400/chapter3.html
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• We will draw isotherms at 5° intervals (15°, 20°, 25°, etc.) for problems part two.
• An isotherm will pass through any point with the same value as the isotherm, but between higher and lower values.
• On one side of the line, the temperatures will be higher than the value of the isotherm, while on the other side, temperatures will be lower.
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Drawing Isolines
• Drawing isolines involves interpolation (estimating values between two known values).– For example, the 15° isotherm passes between the
14° and 16° locations, while the 27° location is about half way between the 25° and 30° isotherms.
• Figure two shows the completed isotherm map. – Notice that isotherms show the spatial pattern of
temperature more clearly than the temperatures of the cities alone.
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http://www.middleschoolscience.com/isotherms.htm
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Isolines: More Information
• Isolines are a graphical tool used to denote geographic lines of equal value.
• Isolines may also be thought of as contour lines showing increasing/decreasing trends of a value of interest i.e. rainfall, elevation, temperature.
• Any points falling on the same isoline will have the same value associated with that isoline.
• Isolines may be used to depict many values which may be of geographic importance.
• Typically isolines of a certain value will be named using the iso- prefix followed by the name of the feature being illustrated.
• Some of the more important types are listed on the following slide.
http://www.clas.ufl.edu/users/kastofan/isolinenotes.htm
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Types of Isolines
• Isoheights – lines of equal elevation or topographic contours.– Isoheights are lines of equal elevation.
• Typically found on topographic maps like USGS topo quadrangles.• Isoheights are useful for observing elevation variations and profiles.
• Isobars – lines of equal atmospheric pressure (weather maps).
• Isotherms – lines of equal temperature.• Isobaths – lines of equal depth or bathymetry.• Isohaline – lines of equal salinity.• Isopycnals – lines of equal rainfall.• Isotachs – lines of equal wind speed.
http://www.clas.ufl.edu/users/kastofan/isolinenotes.htm
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Isoline Trends
• Spatial trends may be interpreted through isolines.• Increases/decreases in the values of interest may be
determined from isolines.• The relative increase/decrease of the values of interest
may also be determined.• The value difference between any two consecutive
isolines is the contour interval.• The relative increase/decrease of a certain value may
also be determined.• Tight spacing between isolines depict relatively sharp
increases/decreases in values.• Wide spacing between isolines depict relatively small
increases/decreases in values.
http://www.clas.ufl.edu/users/kastofan/isolinenotes.htm
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Contour Lines
• Isotherms and Isobars are used to show equal lines of temperature and pressure. Studying landforms involves another kind of isoline, contour lines.
• Contour lines are lines that connect points of equal elevation.
• Contour lines enable us to study the topography of a region from a two-dimensional map.– Figure One show a simple contour line map and a
profile cross section through the landscape.
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http://raider.muc.edu/~mcnaugma/Topographic%20Maps/contour.htm
Simple Contour Line Map and Profile
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Figure Two
• Figure Two shows a fictitious landscape and a contour line map of the same landscape with various elevations and features labeled.
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Contour Line Rules1. A contour line connects points of equal elevation.2. The difference in elevation between two contour lines is known as the contour
interval. 3. Usually every fifth contour line is a darker index contour. 4. Elevations on one side of a contour line are higher than on the other side.5. Contour lines never cross one another although they may touch at a vertical cliff.6. Contour lines have no beginning or end, every line closes on itself either on or off
the map.7. Uniformly spaced contours indicate a uniform slope.8. If spaced far apart, contour lines indicate a gentle slope. If spaced closed
together, they represent a steep slope.9. When crossing a valley or gully, a contour line makes a “v” pointing uphill.10. When crossing a spur or a ridge running down the side of a hill, a contour line
makes a “v” pointing downhill.11. A contour line that closes within the limits of the map represents a hill or rise. The
land within the closed contour is higher than the land outside the closed contour.12. The top of a hill shown with closed contour lines is higher than the uppermost
closed contour, but lower than the next highest contour that hasn’t been shown on the map.
13. A small depression is represented by a closed contour line that is hachured on the side leading into the depression. Hachured contours are called depression contours.