Contouring Data

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Contouring Data

• R. Heath Boucek
• Master of GIS, Not Power Point.
• April 1, 2003

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Contouring Data The Basics

• Contours are lines that connect points of equal
  value (such as elevation, temperature,
  precipitation, pollution, or atmospheric
  pressure).

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More of the Basics

• Contour lines are a familiar way of representing
  surfaces on maps.
• The distribution of the lines show how values
  change across a surface. Where there is little
  change in a value, the lines are spaced further
  apart. Where the values rise or fall rapidly, the
  lines are closer together.

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Some More of the Basics

• Contour lines that cross streams flowing through
  valleys of noticeable relief will form a V-shaped
  deflection with the apex of the V pointing
  upstream
• The rule that states a V will always point
  upstream is the RULE of V's.

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A Little More of the Basics

• Even though contours are a common way of
  representing surfaces on maps they are a poor
  surface model for computers.
• Despite this you can still create contour lines
  for a whole surface, or you can create a single
  contour that passes through a certain point.

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Why Do We Use Map Contours?

• You can identify which areas have the same value
  by following a contour line.
• You can get a general impression of the gradation
  values by looking at the spacing of contours.
• Contour lines are the means of relating the
  vertical dimension (the third dimension) of the
  topography of an area to the two-dimensional
  surface of a topographic map.
• Allows you to view a flat image in 3-D

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Examples of Ways to Use Contouring

• finding the location of atmospheric and oceanic
  fronts,
• locating potential regions of severe
  thunderstorms,
• tracking hurricanes,
• tracking the movement of pollutants.
• tracing water movement in the oceans

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The Contour Function The Basics

• The contour function allows you to create
  contours for an entire dataset.
• Used primarily with elevation
• The value which you begin generating contours is
  The Base Contour.
• Contours are generated above and below the base
  contour as needed to cover entire range of
  values.

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More of the Basics

• The specified distance between contour polylines
  is The Contour Interval .
• Every fifth contour line is printed thicker, and
  then marked with its elevation for reference this
  is The Index Contour .
• The Contour Function is useful and fun!

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Deriving Contours The How To.
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The How To

• Step 1 Click on 3-D Analyst, point to Surface
  Analysis, and click Contour
• Step 2 Click on Input surface and click the
  surface you want to contour

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More of The How To

• Step 3 Set a Contour interval
• Step 4 Set the Base contour to start contouring
  from or leave the default of 0.

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And More of The How To

• Step 5 If needed, set a value for the Z-
  factor.
• Step 6 Change the name for the output or leave
  the default if you wish. This creates a dataset
  for later use.

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And Finally,Some More of The How To

• Step 7 Click OK
• Step 8 Check Your Results

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Creating a single contour

• Step 1 Click the Create Contours button .
• Step 2 Click the surface at the point where you
  want the contour.
• Step 3 The contour is added as a 3D polyline
  graphic.
• Step 4 Admire your work.

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Questions? Comments? Physical Abuse?
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Sources

• ArcGIS Desktop Help
• http//cimss.ssec.wisc.edu/wxwise/contour/contour1
  .html
• Very cool website
• http//www.uta.edu/paleomap/geol1435/contour.htm
• http//geoweb.tamu.edu/courses/geol101/lab/topo_ma
  ps/tsld010.htm