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Isolines and contour lines


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Isolines and contour lines

  1. 1. Isolines and Contour Lines
  2. 2. Isolines <ul><li>To map particular characteristics of an area, such as elevation, the amount of rainfall, or the temperature isolines are often used. </li></ul><ul><li>An isoline is a line on a map that connects points of equal value. </li></ul>
  3. 3. Isolines <ul><li>For example contour lines on topographic maps are isolines that show elevation. </li></ul><ul><li>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 </li></ul>
  4. 4. Basic Rules of isolines <ul><li>An isoline connects points on a map where the value of some phenomenon is the same. </li></ul><ul><li>Isolines are drawn at regular intervals. </li></ul><ul><ul><li>For example every 5° of temperature difference. </li></ul></ul><ul><li>Isolines are always closed lines, although the often close beyond the margins of a map. </li></ul><ul><li>Isoline NEVER cross each other. </li></ul><ul><li>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. </li></ul><ul><li>Values inside a closed isoline are either higher or lower than those outside the close isoline </li></ul><ul><ul><li>It is usually clear which is the case based on the pattern of adjacent isolines. </li></ul></ul>
  5. 5. Figure One <ul><li>This drawing will help illustrate how isotherms are drawn. </li></ul><ul><li>Figure One shows a simple map with temperatures with temperatures plotted for 17 different cities. </li></ul>
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  7. 7. <ul><li>We will draw isotherms at 5° intervals (15°, 20°, 25°, etc.) for problems part two. </li></ul><ul><li>An isotherm will pass through any point with the same value as the isotherm, but between higher and lower values. </li></ul><ul><li>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. </li></ul>
  8. 8. Drawing Isolines <ul><li>Drawing isolines involves interpolation (estimating values between two known values). </li></ul><ul><ul><li>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. </li></ul></ul><ul><li>Figure two shows the completed isotherm map. </li></ul><ul><ul><li>Notice that isotherms show the spatial pattern of temperature more clearly than the temperatures of the cities alone. </li></ul></ul>
  9. 9. Extra Credit Opportunity: Draw in the isolines for 5 points
  10. 10. Isolines <ul><li>Isolines are a graphical tool used to denote geographic lines of equal value. </li></ul><ul><li>Isolines may also be thought of as contour lines showing increasing/decreasing trends of a value of interest i.e. rainfall, elevation, temperature. </li></ul><ul><li>Any points falling on the same isoline will have the same value associated with that isoline. </li></ul><ul><li>Isolines may be used to depict many values which may be of geographic importance. </li></ul><ul><li>Typically isolines of a certain value will be named using the iso- prefix followed by the name of the feature being illustrated. </li></ul><ul><li>Some of the more important types are listed on the following slide. </li></ul>
  11. 11. Types of Isolines <ul><li>Isoheights – lines of equal elevation or topographic contours. </li></ul><ul><ul><li>Isoheights are lines of equal elevation. </li></ul></ul><ul><ul><ul><li>Typically found on topographic maps like USGS topo quadrangles. </li></ul></ul></ul><ul><ul><li>Isoheights are useful for observing elevation variations and profiles. </li></ul></ul><ul><li>Isobars – lines of equal atmospheric pressure (weather maps). </li></ul><ul><li>Isotherms – lines of equal temperature. </li></ul><ul><li>Isobaths – lines of equal depth or bathymetry. </li></ul><ul><li>Isohaline – lines of equal salinity. </li></ul><ul><li>Isopycnals – lines of equal rainfall. </li></ul><ul><li>Isotachs – lines of equal wind speed. </li></ul>
  12. 12. Isoline Trends <ul><li>Spatial trends may be interpreted through isolines. </li></ul><ul><li>Increases/decreases in the values of interest may be determined from isolines. </li></ul><ul><li>The relative increase/decrease of the values of interest may also be determined. </li></ul><ul><li>The value difference between any two consecutive isolines is the contour interval. </li></ul><ul><li>The relative increase/decrease of a certain value may also be determined. </li></ul><ul><li>Tight spacing between isolines depict relatively sharp increases/decreases in values. </li></ul><ul><li>Wide spacing between isolines depict relatively small increases/decreases in values. </li></ul>
  13. 13. Contour Lines <ul><li>Isotherms and Isobars are used to show equal lines of temperature and pressure. Studying landforms involves another kind of isoline, contour lines. </li></ul><ul><li>Contour lines are lines that connect points of equal elevation. </li></ul><ul><li>Contour lines enable us to study the topography of a region from a two-dimensional map. </li></ul><ul><ul><li>Figure One show a simple contour line map and a profile cross section through the landscape. </li></ul></ul>
  14. 14. Simple Contour Line Map and Profile
  15. 15. Figure Two <ul><li>Figure Two shows a fictitious landscape and a contour line map of the same landscape with various elevations and features labeled. </li></ul>
  16. 18. Contour Line Rules <ul><li>A contour line connects points of equal elevation. </li></ul><ul><li>The difference in elevation between two contour lines is known as the contour interval. </li></ul><ul><li>Usually every fifth contour line is a darker index contour. </li></ul><ul><li>Elevations on one side of a contour line are higher than on the other side. </li></ul><ul><li>Contour lines never cross one another although they may touch at a vertical cliff. </li></ul><ul><li>Contour lines have no beginning or end, every line closes on itself either on or off the map. </li></ul><ul><li>Uniformly spaced contours indicate a uniform slope. </li></ul><ul><li>If spaced far apart, contour lines indicate a gentle slope. If spaced closed together, they represent a steep slope. </li></ul><ul><li>When crossing a valley or gully, a contour line makes a “v” pointing uphill. </li></ul><ul><li>When crossing a spur or a ridge running down the side of a hill, a contour line makes a “v” pointing downhill. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>
  17. 19. Topographic Map Questions <ul><li>What is the contour interval on the Cucamonga Peak Quadrangle? </li></ul><ul><li>What is the elevation of the Etiwanda Fire Station? </li></ul><ul><li>What is the elevation of Day Canyon Station? </li></ul><ul><li>Find the 1320 foot interval at the bottom right corner of the map. Does it close in on itself, or is it interrupted by the edge of the map? </li></ul><ul><li>Find Cucamonga Peak on the map. Which side it steeper? </li></ul><ul><li>Find Day Creek on the map. In what compass direction does this creek flow? </li></ul>