Isolines and contour lines
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Isolines and contour lines






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    Isolines and contour lines Isolines and contour lines Presentation Transcript

    • Isolines and Contour Lines
    • 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.
    • 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
    • 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.
    • Figure One
      • This drawing will help illustrate how isotherms are drawn.
      • Figure One shows a simple map with temperatures plotted for 17 different cities.
      • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • Simple Contour Line Map and Profile
    • Figure Two
      • Figure Two shows a fictitious landscape and a contour line map of the same landscape with various elevations and features labeled.
    • 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.