Isolines and contour lines
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Isolines and contour lines






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Isolines and contour lines Presentation Transcript

  • 1. Isolines and Contour Lines
  • 2. 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.
  • 3. 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
  • 4. Basic Rules of isolines
    • An isoline connects points on a map where the value of some phenomenon is the same.
    • Isolines are drawn at regular intervals.
      • For example every 5° of temperature difference.
    • Isolines are always closed lines, although the often close beyond the margins of a map.
    • Isoline NEVER cross each other.
    • 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.
    • 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.
  • 5. Figure One
    • This drawing will help illustrate how isotherms are drawn.
    • Figure One shows a simple map with temperatures plotted for 17 different cities.
  • 6.
  • 7.
    • 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.
  • 8.  
  • 9. 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.
  • 10.
  • 11.  
  • 12. 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.
  • 13. 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.
  • 14. 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.
  • 15. 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.
  • 16. Simple Contour Line Map and Profile
  • 17. Figure Two
    • Figure Two shows a fictitious landscape and a contour line map of the same landscape with various elevations and features labeled.
  • 18.  
  • 19.  
  • 20. Contour Line Rules
    • A contour line connects points of equal elevation.
    • The difference in elevation between two contour lines is known as the contour interval.
    • Usually every fifth contour line is a darker index contour.
    • Elevations on one side of a contour line are higher than on the other side.
    • Contour lines never cross one another although they may touch at a vertical cliff.
    • Contour lines have no beginning or end, every line closes on itself either on or off the map.
    • Uniformly spaced contours indicate a uniform slope.
    • If spaced far apart, contour lines indicate a gentle slope. If spaced closed together, they represent a steep slope.
    • When crossing a valley or gully, a contour line makes a “v” pointing uphill.
    • When crossing a spur or a ridge running down the side of a hill, a contour line makes a “v” pointing downhill.
    • 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.
    • 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.
    • 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.