Someone learning to read a language that has an unfamiliar alphabet (e.g.
a child with any written language, or an adult American learning Russian)
has to look carefully at each individual letter at first. In time, however,
the unit of perception becomes the syllable, then the whole word, and
perhaps even a group of words. The speed of reading increases dramatically
as the mind learns what information is essential and what can be ignored.
Likewise, a beginner is often overwhelmed by the amount of detail on
a standard topographic map, whereas a skilled map reader seldom bothers
to trace individual contours. Taken as a group, contour lines often form
patterns that indicate familiar terrain features. Over the years, people
have developed a number of ways to classify terrain elements. This section
introduces a simple but useful classification of basic landforms. The
small X on each idealized contour map shows the point from which four
people m might try to walk in different directions, as described in the
text paragraphs. The four paths are always at right angles to each other,
but the set is oriented so that one individual goes directly up or down
the steepest slope.
||1) Plain (flat) - a generally level area, with few
contour lines and no significant change in elevation in any direction.
If four people walked away in all directions from a point on a plain,
all four would remain at about the same elevation.
||2) Slope -- a flat area that is tilted, not level.
Contour lines on a slope are generally straight and parallel to each
other. If four people walked away from each other on a slope, one
person would go downhil, one would climb, and two would stay at the
||3) Summit (peak) - the highest point in a given area.
At least one contour line goes all the way around a summit. If four
people walked in different directions from a point on a summit, they
would all go dowriill. If they descend at the same rate, the summit
||4) Ridge (crest) - a long and narrow high area. Contour
lines are generally straight and parallel to each other. If four people
walked away from a point on a ridge, two would go downhill and two
would stay at the same elevation.
||5) Spur (nose) a tilted ridge, where the contours form
a roughly parallel set of rounded 'V' shapes. If four people walked
away from a point on a spur, one would climb, one go gently downhill
and two would have to descend more steeply.
||6) Cliff -- an abrupt and very steep slope, with crowded
parallel contours. If four people walked away from a point near the
top of a cliff, two would stay about the same level, one could stay
level or climb, and one may not survive the fall.
||7) Bench (terrace) - a level area on a slope, with
parallel straight contours. If four people walked away from a point
on a bench, all would start out level, but one would soon climb and
another would go downhill, while the other two stayed generally at
the same level.
||8) Valley - a long and narrow low area, lie an upside-down
ridge. The contour lines are often straight and parallel to each other,
although a valley, like a edge, can curve. If four people walked away
from a point in a valley, two would stay at about the same elevation
and two would go uphill.
||9) Draw -- a tilted low area, like an inverted spur.
Contour lines form a parallel set of rounded "I' shapes. If four
people walked away from a point in a draw, two would climb steeply,
one would go more gently uphill, and one would descend.
||103 Depression (hole or pit) - the lowest point in
a local area (an upside-down summit). At least one contour line completely
encircles a depression; tiny hachures indicate the downhil direction.
Four people wanting away from a point at the bottom of a dep depression
would all have to go uphill.
||11) Butte -- hill with a flat top and steep sides,
marked by closely spaced concentric contours that encircle a level
area with few lines. If four people tried to walk away from each other
on a butte, no one could walk too far! (A big butte is called a mesa).
||12) Pass (saddle) -- a low point in a high area, with
contours that look like a combination of two spurs and two draws.
If four people walked away from a point in a pass, two would go downhill
and two would have to climb.
||13) Fan -- a wide spur, where the contour lines form
a set of nested arcs or concentric half-circles. If four people walked
away from each other on a fan, one would climb gently uphill and the
other three would descend slowly.
||14) Scarp (cuesta or hogback) - an asymmetrical ridge,
with one slope significantly steeper than the other. If four people
walked in opposite directions from a point on a scarp, two would stay
nearly level, one would go gently downhill, and one would go s steeply
These topographic positions (terrain elements, or topographic features)
do not exist in isolation. On the contrary, they tend to occur in more-or-less
predictable groups (associations) of related landforms. Two summits, for
example, usually are separated by a pass, which in turn serves as the top
of two draws. Similarly, a long draw leading out onto a plain in a dry region
will usually have a fan where it leaves the hillier area In many cases,
these associations of topographic features can provide some valuable clues
about the geologic structure that underlies the landscape. At the same time,
however, the close association of different topographic features can make
it difficult to separate one feature from another (or even to decide whether
a particular f feature actually exists in an area). In short, the identification
of topographic features is at least partly an arbitrary process, just like
all other aspects of the language of maps.
To complicate things further, the scale of individual terrain elements
can vary widely in different regions. For example, a pile of dirt exposed
to the rain in North Carolina will develop an intricate set of draws and
tiny fans, often no more than a few f feet across. The same process working
a long time in the radically different climate and rock material of Nevada
can build fans that are many miles wide and thousands of feet thick. With
practice, a map reader learns what shapes and saplings of contour lines
are normal within a given region. Perhaps even more important, a skilled
reader can "read between the contour lines" and see what the
slope actually is lie. For example, a wiggly contour line may indicate
a rough and rocky slope with many irregularities too small to show with
individual contour lines.
This Material was adapted from: The Language of Maps by Philip J. Gersmehl,
N.C.G.E. Pathways in Geography Series, No. 1, 1991. pp.60-62.