Fields isolines gradients and topographic maps
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Fields, Isolines, Gradients and Topographic Maps. Earth Science – Notes #3. Fields. A field is any region of space, 2-D or 3-D, that has a measurable value at every point. For example, one can measure the elevation of a staircase at every stair, so the staircase is a field.

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Fields, Isolines, Gradients and Topographic Maps

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Fields isolines gradients and topographic maps

Fields, Isolines, Gradients and Topographic Maps

Earth Science – Notes #3


Fields

Fields

  • A field is any region of space, 2-D or 3-D, that has a measurable value at every point.

  • For example, one can measure the elevation of a staircase at every stair, so the staircase is a field.

  • Fields may be represented graphically


Fields1

Fields

  • Example: the temperature field in the oceans of the world


Isolines

Isolines

  • Isolines literally mean same (iso-) lines.

  • They are lines that connect points of equal value in a given field.

  • Common examples of isolines are:

    • Isotherms – temperature

    • Isobars – atmospheric pressure

    • Contour lines – elevation


Isolines1

Isolines

  • These are isobars on a weather map


Gradients

Gradients

  • A gradient is the rate of change of a field value from place to place within a field.

  • Also called slope.

  • Spacing of isolines – the closer together the higher the gradient

  • Calculated by

    • gradient = change in field value

      distance

      *Page 1 in ESRT*


Topographic maps

Topographic Maps

A topographic map is a representation of a three-dimensional surface on a flat piece of paper


Topographic maps1

Topographic Maps

  • AKA Contour maps.

  • Models that show the elevation field of an area of the Earth.

  • Elevation is vertical distance above sea level.

  • Useful in many aspects of outdoor life (hiking) and environmental planning (roads, buildings, drainage)

  • Drawn with contour lines


Contour lines

Contour lines

  • Contour lines connect points of equal elevation

  • If you walk along a contour line your elevation will not change

  • The closer together the contour lines appear on a topographic map, the steeper the slope


Contour gradient

Contour Gradient

  • The rate of elevation change from place to place. Also called steepness or slope.

  • Calculated by the formula

    • gradient = change in elevation

      distance

      **The closer the lines, the steeper the land**


Gradient

Gradient

  • Closer

  • Steeper

  • Further

  • Gentler


Contour interval

Contour Interval

  • The vertical change in elevation between each contour line

  • 20 ft. on this map


Topographic maps misc

Topographic maps misc.

Rule of V’s

-When contour lines cross a stream they bend upstream. The stream flows opposite the V.


Topographic maps misc1

Topographic maps misc.

  • Index contours

    thicker than others

    and give elevation.

  • Benchmarks are

    permanent markers

    of elevation used

    as reference points.


Map scale

Map Scale

  • Scale is the ratio of a horizontal distance between the points on a map and the actual distance between the two points on the Earth.

  • Scales may be verbal (one inch equals a mile), fractional (1:5000), or graphical


Map direction

Map Direction

  • Top of a map is usually North, bottom is South, right is East, and left is West.

  • Maps commonly include a North arrow or compass rose.

    W E

    S

N


Fields isolines gradients and topographic maps

Depression Contour Lines

  • a.k.a. hachure lines

  • Show holes or depressions in the ground surface


Contour profile

Contour Profile

  • A side-view or cross-section along a line on a map.

  • A profile is constructed by plotting elevations versus distance on a graph.


Fields isolines gradients and topographic maps

Vertical Exaggeration

  • Profiles are typically exaggerated to show vertical features

  • This is the number of times larger an object has been made to appear in the vertical direction

  • Calculated by dividing the horizontal scale by the vertical scale


Fields isolines gradients and topographic maps

Used to show vertical details not easily seen in a profile.


Rules of contour lines some basic rules or facts about contour lines are listed below

Rules of Contour Lines — Some basic rules or facts about contour lines are listed below.

1) Where a contour line crosses a stream or valley, the contour bends to form a "V" that points upstream or valley. In the upstream direction the successive contours represent higher elevations.

2) Contours near the upper parts of hills form closures. The top of a hill is higher than the highest closed contour.

3) Hollows (depressions) without outlets are shown by closed, hatched contours. Hatched contours are contours with short lines on the inside pointing downslope. The bottom of the hollow is lower than the lowest closed contour.


Fields isolines gradients and topographic maps

  • 4) Contours are widely spaced on gentle slopes. 5) Contours are closely spaced on steep slopes. 6) Evenly spaced contours indicate a uniform slope.

  • 7) Contours do not cross or intersect each other, except in the rare case of an overhanging cliff.

  • 8) All contours eventually close, either on a map or beyond its margins.

  • 9) A single higher elevation contour never occurs between two lower ones, and vice versa. A change in slope direction is always determined by the repetition of the same elevation either as two different contours of the same value or as the same contour crossed twice.


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