Relief and Vertical interval

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Relief and Vertical interval

• How to understand the shape of ground
• How to interpret 2-D maps as 3-D shapes
• Learn how to identify and describe landforms

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Why bother? You ask

• It is the most important map reading skill
• It will help you work out where you are
• It will help you plan the easiest or safest route
  to your destination
• It will stop you looking like an idiot when you
  are a section commander and are left holding the
  map!

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Relief

• Relief is the word that describes the rise and
  fall of the land. Easy to see in reality but
  difficult to display on a 2-D surface.
• there are different methods used to display
  relief on a map

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layering

• Shading or tinting to show all areas between a
  certain height

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hachures
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Hill shading
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contours

• Contour interval (the distance between contour
  lines) is determined by terrain and map scale
• Index contours are symbolized as wider lines and
  usually every 5th contour.
• Form lines are approximate elevations (not
  accurately surveyed).
• Depression contours (enclosing lower land) are
  drawn with small tick marks inside.

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Interpretation of contours

• Imagine a glass table with four layers
• The vertical height between the layers is
  represented by the numbers on the contours
• Each contour overlayed on a single layer retains
  the information

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Interpretation of contours

• The closer the lines are together the steeper the
  slope
• Walking left to right along this hill would
  include slopes of different steepness

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Up or down the slope?

• It is sometimes tricky to work out what is a
  positive, uphill slope and what is a negative,
  downhill slope.
• If there are numbered contours nearby it is easy
  is easy
• You often need to look at the position of rivers
  and streams or ponds to determine the direction
  of slope

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Convex and concave slopes

• Walking up hill a convex slope gets less steep
  but a concave gets steeper
• Looking at contours you can identify these two
  types of slope
• dead ground is a key tactical consideration

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Convex and concave
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Dead ground

• Observing from the top of a convex slope the
  ground below is out of sight and is referred to
  as dead ground.
• This gives a stealthy approach or cover from fire

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Relief features
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Spurs

• Spurs are like the ends of your fingers layed on
  the table
• High ground falling away to lower ground on three
  sides

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ridges

• Ridges are narrow linear features of high ground
  with steep slopes either side

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Re-entrant

• This is a miniature valley, often between two
  spurs, like the gap between your fingers on the
  table.

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saddle

• A saddle is the lower ground between two areas of
  higher ground

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Valley

• We all know what a valley looks like. They come
  in all shapes.
• Not all valleys have rivers at the bottom
• Here is a steep sided one

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Separate hills
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summary

• Contours are the most important feature of a map
• It takes experience and practise to interpret
  them easily
• You can visualise relief by looking at the
  contours and placing other features in context
• Navigation is nearly impossible without an
  understanding of relief