Topographic Maps
Topographic maps are important tools for studying the earth's surface, not only for
geologists, but also for engineers, foresters, land use planners, hikers, ... virtually
anyone who travels outdoors. Topographic maps summarize the three dimensional
topography of the earth's surface on two dimensional pieces of paper (or computer
screens).
These web pages are designed to be an introduction to topographic maps for geology
students. Additional information on topographic maps can be found at the USGS web
site and the Topozone web site.
Let’s use the area around Squaretop Mountain (shown below) to illustrate the power of
topographic maps. Squaretop Mountain is located in the Wind River Mountains of
Wyoming. The photo of Squaretop Mountain (taken looking south) shows some of the
important topographic features of the mountain. From the photo we can see that the top
of Squaretop Mountain is capped by a relatively wide flat area (which gives the
mountain its name). This area is not horizontal; instead it slopes down to the west (to
the right in the photo). Surrounding this flat area are extremely steep slopes (cliffs). At
the base of these cliffs the slope decreases (though it is still very steep).
A skilled reader (well not really even that skilled) of topographic maps could make the
same observation from the map without even seeing the photo. The slightly sloping top,
the cliffs, and the lesser slopes on this mountain are all evident on the topographic map.
By the time you have gone through these web pages you should be able to read the
topographic well enough to recognize topographic features of Squaretop Mountain.
But if we can determine the same information from the photograph why do we need to
worry about learning to read topographic maps? Well, first we may not always have a
photograph, or we may be looking at areas where the topography will not show up well
in a photograph. Topographic maps are much more widely available. Second the
topographic map provides more information. From our map of Squaretop Mountain we
can measure the size of the top part of the mountain (just under 1 km x 0.5 km). We can
determine the elevation of the submit of Squaretop Mountain (11695 ft) and estimate its
relief (height above the valley floor, ~3500 ft). We can also study the topography from
parts of the mountain that can't be seen in the photograph. For example from the map
we can see that the slopes that are not as steep on the south side of the mountain (the
side that is behind the mountain in the photograph), information that might prove very
useful if we were trying to climb a mountain. None of this information is available from
the photograph. Instead it is the topographic map that provides us with the detailed
information we often seek as geologist.
Common symbols on a Topo map
A topographic map is a map that shows topography and features found on the earth's
surface. Like any map it uses symbols to represent these features. Let’s look at a
section of a topographic map showing the area around Spruce Knob in West Virginia.
Spruce Knob is the highest point in West Virginia.
This section of a topographic
map illustrates many of the
common symbols used on topo
maps. The map is repeated
below with many of these
symbols labeled.
Some of the more common and
important topographic map
symbols have been pointed out
by the purple arrows.
First let’s recognize that map
symbols are color coded.
Symbols in green indicate
vegetation, symbols in blue
represent water, brown is used
for topographic symbols,
manmade features are shown in
black or red. Let’s look at the
symbols labeled in the map
above:
Contour Lines
Contour lines are lines that
indicate elevation. These are the
lines that show the topography
on the map. They are discussed in more detail in the next section. Contour lines are
shown in brown. Two types of contour lines are shown. Regular contour lines are the
thinner brown lines, index contour lines are the thicker brown lines. The numbers
written in brown along the contour lines indicate elevation of the line. For this map
elevation is in feet above sea level.
Map Scale
Map scale represents the relationship between distance on the map and the
corresponding distance on the ground. The scale on the topo map is found at the
bottom center of the map.
Scale is represented in two different ways on a topographical map. The first is a ratio
scale. The ratio scale on this map is 1:24,000. What it means is that one inch on the
map represents 24,000 inches on the ground. Or one centimeter on the map represents
24,000 centimeters on the ground (or any other unit you want to choose). Below the
ratio scale is a graphic scale representing distance in miles, feet and meters. The
graphic scale can be used to make fast estimates of distances on the map.
VERBAL SCALE
The simplest form of map scale is a VERBAL SCALE. A verbal scale just states what
distance on the map is equal to what distance on the ground, (i.e. 1 inch = 2000 feet
from our example above) Though verbal scales are easy to understand, you usually will
not find them printed on topographic maps. Instead our second type of scale is used.
FRACTIONAL SCALE
Fractional scales are written as fractions (1/62500) or as ratios (1:62500). Unlike verbal
scales, fractional scales do not have units. Instead it is up to the map reader to provide
his/her own units. Allowing the reader of the map to choose his/her own units provides
more flexibility but it also requires a little more work. Basically the fractional scale
needs to turned in to a verbal scale to make it useful.
First lets look at what a fractional scale means. A fractional scale is the ratio of map
distance to the equivalent distance on the ground using the same units for both. It is
very important to remember when we start changing a fractional scale to a verbal scale
that both the map and ground units start out the same. The smaller number of the
fractional scale is the distance on the map, the larger number in the scale is the
distance on the ground.
So if we take our example scale (1:62500) we can choose units we want to measure
distance in. Lets chose inches. We can rewrite our fractional scale as a verbal scale:
1 inch on the map = 62500 inches on the ground.
We can do the same thing with any unit of length. Some examples of verbal scales
produced using various units from a 1:62500 fractional scale are given in the table:
UNITS
VERBAL SCALE
inches
1 inch on the map = 62500 inches
on the ground.
feet
1 foot on the map = 62500 feet on
the ground
cm
1 cm on the map = 62500 cm on
the ground
m
1 m on the map = 62500 m on the
ground
Notice the pattern. The numbers are the same, only the units have changed. Note that
the same units are used on both sides of each verbal scale.
While these verbal scales are perfectly accurate, they are not very convenient. For
example we may want to measure the distance on a map in inches, we rarely want to
know the distance on the ground in inches. If someone asks you the distance from
Cleveland to Columbus they do not want the answer in inches. Instead we need to
convert our verbal scale into more useful units.
Lets take our example (1 inch on the map = 62500 inches on the ground). Measuring
map distance in inches is OK, but we need to come up with a better unit for measuring
distance on the ground. Lets change 62500 inches into the equivalent in feet (I choose
feet because I remember that there are 12 inches in 1 foot). If we multiply 62500 inches
by the fraction (1 ft / 12 in) inches in the numerator and denominator cancel leaving an
answer in feet. Remember, since 1 ft = 12 inches, multiplying by (1 ft / 12 in) is the
same as multiplying by 1. The result of this multiplication gives:
62500 inches x (1 ft / 12 in)= 5208.3 ft
So we can rewrite our verbal scale as 1 inch on the map = 5208.3 feet on the ground.
This is a perfectly valid verbal scale, but what if we wanted to know the distance in miles
instead of feet. We just need to change 5208.3 feet into miles (we could change 62500
inches into miles but I never remember how may inches are in 1 mile). Knowing that
there are 5280 feet in a mile:
5208.3 ft x (1 mi/5280 ft) = 0.986 mi.
So our verbal scale would be: 1 inch on the map = 0.986 miles on the ground. For most
practical purposes we can round this off to 1 inch on the map ~ 1 mile on the ground,
making this scale much easier to deal with.
So for any fractional scale we can choose the same units to assign to both sides and
then convert those units as we see fit to produce a verbal scale. Given all the possible
map scales and all the possible combination of units that can be used it may seem that
scales on topographic maps are very complicated. In fact there are only a few scales
commonly used, and each is chosen to allow at least one simple verbal scale. The
most common fractional scales on United States topographic maps and equivalent
verbal scales are given in the table below.
FRACTIONAL SCALE
SIMPLE VERBAL
SCALE
1:24000
1 in = 2000 ft
1:62500
1 in ~ 1 mi
1:100000
1 cm = 1 km
1:125000
1 in ~ 2 mi
1:250000
1 in ~ 4 mi
BAR SCALE
A bar scale is just a line drawn on a map of known ground length. There are usually
distances marks along the line. Bar scales allow for quick visual estimation of distance.
If more precision is needed just lay the edge of a piece of paper between points on the
map that you want to know the distance between and mark the points. Shift the paper
edge to the bar scale and use the scale like a ruler to measure the map distance.
Bar scales are easy to use, but there is one caution. Look at the typical bar scale drawn
below. Note that the left end of the bar is not zero. The total length of this bar is FIVE
miles, not four miles. A common error with bar scales is to treat the left end of the line
as zero and treat the whole bar as five miles long. When using a bar scale to measure
distances on a map, pay attention to where the zero point is.
In addition to their ease of use, there is one other advantage of a bar scale. If a map is
being enlarged or reduced, a bar scale will remain valid if it is enlarged and reduced by
the same amount. Fractional and verbal scales will not be valid. This is a problem with
the maps you are looking at on this web site. The actual scale of the map will vary
depending on your computer monitor and its setting.
Contour Lines
Contour lines are lines drawn on a
map connecting points of equal
elevation. If you walk along a
contour line you neither gain or
lose elevation.
Picture walking along a beach
exactly where the water meets the
land (ignoring tides and waves for
this example). The water surface
marks an elevation we call sea
level, or zero. As you walk along
the shore your elevation will
remain the same; you will be
following a contour line. If you stray from the shoreline and start walking into the ocean,
the elevation of the ground (in this case the seafloor) is below sea level. If you stray the
other direction and walk up the beach your elevation will be above sea level (see
diagram at right).
The contour line represented by the shoreline separates areas that have elevations
above sea level from those that have elevations below sea level. We refer to contour
lines in terms of their elevation above or below sea level. In this example the shoreline
would be the zero contour line.
Contour lines are useful because they allow us to show the shape of the land surface
(topography) on a map. The two diagrams below illustrate the same island. The
diagram on the left is a view from the side (cross profile view) such as you would see
from a ship offshore. The diagram at right is a view from above (map view) such as
you would see from an airplane flying over the island.
The shape of the island is shown by the location of the shoreline on the map.
Remember this shore line is a contour line. It separates areas that are above sea level
from those that are below sea level. The shoreline itself is right at zero so we will call it
the 0 ft. contour line.
The shape of the island is more complicated than the outline of the shoreline shown on
the map above. From the profile it is clear that the islands topography varies (that is
some parts are higher than others). This is not obvious on a map with just one contour
line. But contour lines can have elevations other than sea level. We can picture this by
pretending that we can change the depth of the ocean. The diagram below shows an
island that is getting flooded as we raise the water level 10 ft above the original sea
level.
The new island is obviously smaller than the original island. All of the land that was less
than 10 ft. above the original sea level is now under water. Only land where the
elevation was greater than 10 ft. above sea level remains out of the water. The new
shoreline of the island is a contour line because all of the points along this line have the
same elevation, but the elevation of this contour line is 10 ft above the elevation of the
original shoreline. We repeat this processes in the two diagrams below. By raising
water levels to 20 ft and 30 ft above the original see level we can find the location of the
20ft and 30 ft contour lines. Notice our islands gets smaller and smaller.
Fortunately we do not really have to flood the world to make contour lines. Unlike
shorelines, contour lines are imaginary. They just exist on maps. If we take each of the
shorelines from the maps above and draw them on the same map we will get a
topographic map (see map below). Taken all together the contour lines supply us with
much information on the topography of the island. From the map (and the profile) we
can see that this island has two "high" points. The highest point is above 30 ft elevation
(inside the 30 ft contour line). The second high point is above 20 ft in elevation, but
does not reach 30 ft. These high points are at the ends of a ridge that runs the length of
the island where elevations are above 10 ft. Lower elevations, between the 10 ft
contour and sea level surround this ridge.
With practice we can picture topography by looking at the map even without the cross
profile. That is the power of topographic maps.
Determining Contour Intervals
Contour lines can be drawn for any elevation, but to simplify things, only lines for certain
elevations are drawn on a topographic map. These elevations are chosen to be evenly
spaced vertically. This vertical spacing is referred to as the contour interval. For
example the maps on the previous page used a 10 ft contour interval. Each the contour
lines was a multiple of 10 ft.( i.e. 0, 10, 20, 30). Other common intervals seen on
topographic maps are 20 ft (0, 20, 40, 60, etc), 40 ft (0, 40, 80, 120, etc), 80 ft (0, 80,
160, 220, etc), and 100ft (0, 100, 200, 300, etc). The contour interval chosen for a map
depends on the topography in the mapped area. In areas with high relief the contour
interval is usually larger to prevent the map from having too many contour lines, which
would makes the map difficult to read.
The contour interval is constant for each map. It will be noted on the margin of the map.
You can also determine the contour interval by looking at how many contour lines are
between labeled contours.
Most contour lines on topographic maps are not labeled with elevations. Instead the
reader of the map needs to be able to figure out the elevation by using the labeled
contour lines and the contour interval. On most maps determining contour interval is
easy, just look in the margin of the map and find where the contour interval is printed
(i.e. Contour Interval 20 ft).
For the maps on this web site, however, the contour interval is not listed because we
only have parts of topographic maps, not the whole map which would include the
margin notes. However we usually don't need to be given the contour interval, we can
calculate it from the labeled contours on the map as is done below.
Index Contours
Topographic maps may have many
contour lines. It is not possible to label
the elevation of each contour line. To
make the map easier to read every
fifth contour line vertically is an index
contour. Index contours are shown by
darker brown lines on the map. These
are the contour lines that are usually
labeled.
The example at right is a section of a
topographic map. The brown lines are
the contour lines. The thin lines are
the normal contours, the thick brown
lines are the index contours. Notice
that elevations are only marked on the
thick lines.
Because we only have a piece of the topographic map we can not look at the margin to
find the contour interval. But since we know the elevation of the two index contours we
can calculate the interval ourselves. The difference in elevation between the two index
contours (800 - 700) is 100. We cross five lines as we go from the 700 line to the 800
line (note we don't include the line we start on but we do include the line we finish on).
Therefore if we divide the elevation difference (100) by the number of lines (5) we will
get the contour interval. In this case it is 20. We can check ourselves by counting up
by 20 for each contour from the 700 line. We should reach 800 when we cross the 800
line.
One piece of important information we can not determine from the contour lines on this
map is the units of elevation. Is the elevation in feet, meters, or something else. There
is a big difference between an elevation change of 100 ft. and 100 m ( 328 ft). The
units of the contour lines can be found in the margin of the map. Most topographic
maps in the United States use feet for elevation, but it is important to check because
some do use meters.
Once we know how to determine the elevation of the unmarked contour lines we should
be able determine or at least estimate the elevation of any point on the map.
Using the map below estimate the
elevation of the points marked with
letters Point A = 700
An easy one. Just follow along the
index contour from point A until you
find a marked elevation. On real
maps this may not be this easy. you
may have to follow the index contour
a long distance to find a label.
Point B = 740
This contour line is not labeled. But
we can see it is between the 700 and
800 contour line. From above we
know the contour interval is 20 so if
we count up two contour lines (40) from 700 we reach 740.
Point C ~ 770
Point c is not directly on a contour line. But by counting up from 700 we can see it lies
between the 760 and 780 contour lines. Because it is in the middle of the two we can
estimate its elevation as 770.
Point D = 820
Point D is outside the interval between the two measured contours. While it may seem
obvious that it is 20 above the 800 contour, how do we know the slope hasn't changed
and the elevation has started to back down? We can tell because if the slope stated
back down we would need to repeat the 800 contour. Because the contour under point
D is not an index contour it can not be the 800 contour, so it must be 820.
Is it a Hill or is it a Hole?
Hill or Hole?
Look at the figure to the right. You should be able to
recognize that you are looking at two hills... OR are
you? Let's assume the contour on the lower left is
sea level. Can you figure out the rest of the contour
labels?...
Here the contours have been added (how did you
do?)
Now lets consider another possibility. What if the
closed contours on the right were not representing
a hill but rather a HOLE. Can you see that the
contour shape would be the same, but the labels
would be different? It turns out that there is a way
to determine whether closed contours (ones that
make a complete circle) are a hill or a hole. If they
represent a hole, little lines (called hachure's) are
added which point towards the bottom of the hole.
Now can you predict what the contour labels will be
for the two circles on the right?
CAUTION: keep in mind that if you climb up a hill and cross through an elevation, when
you crest the hill and go back down you must go back down through the same
elevations (contours) as you went through on the way up. Study the figure to the right
and pay close attention to the 300 contour interval.
So the map on the right shows
what a hole would look like.
Notice how the 30 foot contour
lines must be repeated.
Now let's practice what you have learned. Use the map below to answer the questions
on your handout. HINT: The elevation of the coastline (at "A") is sea level.
Reading Elevations
A common use for a topographic map is to determine the elevation at a specified
locality. The map below is an enlargement of the map of the island used in a previous
page (Contour lines). Each of the letters from A to F represent locations for which we
wish to determine elevation. Use the map and determine (or estimate) the elevation of
each of the 5 points. (Assume elevations are given in feet)
Point A = 0 ft
Point A sits right on the 0 ft contour line. Since all points on this line have an elevation
of 0 ft, the elevation of point A is zero.
Point B = 10 ft.
Point B sits right on the 10 ft contour line. Since all points on this line have an elevation
of 10 ft, the elevation of point B is 10 ft.
Point C ~ 15 ft.
Point C does not sit directly on a contour line so we can not determine the elevation
precisely. We do know that point C is between the 10ft and 20 ft contour lines so its
elevation must be greater than 10 ft and less than 20 ft. Because point C is midway
between these contour lines we can estimate the elevation is about 15 feet (Note this
assumes that the slope is constant between the two contour lines; this may not be the
case) .
Point D ~ 25 ft.
We are even less sure of the elevation of point D than point C. Point D is inside the 20
ft. contour line indicating its elevation is above 20 ft. Its elevation has to be less than 30
ft. because there is no 30 ft. contour line shown. But how much less? There is no way
to tell. The elevation could be 21 ft, or it could be 29 ft. There is no way to tell from the
map.
Point E ~ 8 ft.
Just as with point C above, we need to estimate the elevation of point E somewhere
between the 0 ft and 10 ft contour lines it lies in between. Because this point is closer to
the 10 ft line than the 0 ft. line we estimate an elevation closer to 10. In this case 8 ft.
seems reasonable. Again this estimation makes the assumption of a constant slope
between these two contour lines.
Lets go back to the Spruce Knob area and practice reading elevations. On the map
below are 10 squares labeled A through J. Estimate the elevation for the point marked
by each square (make sure to use the point under the square, not under the letter).
Compare your answers to the answers below. Recall that we determined the contour
interval on the previous page.
Elevation is in feet
ELEVATION of Points:
A. 4400 ft Point A sits right on a labeled index contour. Just follow along the contour
line until you reach the label
B. 4720 ft Point B sits on a contour line, but it is not an index contour and its elevation
is not labeled. First, lets look for a nearby index contour. There is one to the south and
east of point B. This contour is labeled as 4600 ft. Next we need to determine if point B
is above or below this index contour. Notice that if we keep going to the southeast we
find contour lines of lower elevations (i.e. 3800 ft.). This means as we move away from
4600 ft. contour line toward point B, we are going up hill. So point B is above 4600 ft.
Count the contour lines from 4600 ft to point B, there are three. Each contour line is 40
ft. (from our previous discussion of the contour interval) so point B is 120 ft. above 4600
ft, that is it is 4720 ft.
C. 4236 ft Point C sits right on a labeled bench mark so its elevation is already written
on the map.
D. Point D is on an unlabeled contour line. From our discussion of point B above, you
can see that point D is on the slope below Spruce Knob. Just above point D is an index
contour. If we trace along this contour line we see its elevation. Since point D is the
next contour line down hill from that elevation, its value will be one contour interval
lower.
E. Like Point A above, Point E is on an index contour. Follow along this contour line
until you come to the label.
F. Point F does not sit on a contour line so we can only estimate its elevation. The
point is circled by several contour lines indicating it is a hill top. First, lets figure out the
elevation of the contour line that circles point F. Starting from the nearest index contour
line (4600 ft) we count up by 40 for the four contour lines. This gives us 4760 ft (4600ft
+ 40 ft, 4 times). Because point F is inside this contour line it must have an elevation
above 4760 ft., but its elevation must be less than 4800 ft, otherwise there would be a
4800 contour line, which is not there. We don't really know the elevation, just that it is
between 4760ft. and 4800ft.
G. In order to determine the elevation of point G we first must recognize it is on the
western slope of Spruce Knob. Looking at the index contours we see that point G is
somewhere between 4000 ft and 4400 ft contours. You do the rest.
H. Point H is circled by a contour line indicating it is the top of a small hill. Its elevation
is determined the same way we determine the elevation of Point F. Keep in mind that
you CANNOT determine the exact value, so for your answer give the appropriate range
as in Point F.
I. ~3980 ft. Point I is also not on a contour line. It is also not on the top of a hill
because a contour line does not encircle it. Instead it is in between to contour lines on
the side of a hill. One of the contour lines is the 4000 ft index contour. The other
contour is 3960 ft contour (40 ft lower, you can tell it is lower because you are moving
toward the stream which is in the bottom of the valley). The elevation of point I is
between 3960ft and 4000ft. Since point I is midway between these two contours we
can estimate its elevation as midway between 3960 and 4000.
J. The elevation of point J is found the same way as the elevation of point I.
Gradient (Slope)
Topographic maps are not just used for determining elevation, they can also be used to
help visualize topography. The key is to study the pattern of the contour lines, not just
the elevation they represent. One of the most basic topographic observation that can
be made is the gradient (or slope) of the ground surface. High (or steep) gradients
occur in areas where there is a large change in elevation over a short distance. Low (or
gentle) gradients occur where there is little change in elevation over the same distance.
Gradients are obviously relative. What would be considered steep in some areas (like
Ohio) might be considered gentle in another (like Montana). However we can still
compare gradients between different parts of a map.
On a topographic map the amount of elevation change is related to the number of
contour lines. Using the same contour interval, the more contour lines over the same
distance indicates a steeper slope. As a result, areas of a map where the contour lines
are close together indicate steeper slopes. Areas with widely spaced contour lines are
gentle slopes. The map below shows examples of areas with steep and gentle
gradient. Note the difference in contour line spacing between the two areas.
Compare the slope of the west side of Spruce Knob with the slope of the east side.
Which side is steeper?
It is possible to calculate the gradient right off the map. Gradient is simply the rise over
the run. Which is to say the elevation change divided by the horizontal distance. Let's
say you parked your car on the road by the end of the white arrow (point "A") on the
Spruce Knob map. Further let's say you want to hike from there straight up to the top of
the Knob (following the white arrow). You need to know two things to determine the
gradient: 1) the horizontal distance and 2) the elevation change.
1. The elevation change (or "rise") is simply the difference between the
elevation of your car at point "A" (which we can see as 4200' because it
sits right on a contour line) and the elevation at the top of Spruce Knob
(which is labeled as 4861'). So the elevation change is 4861 - 4200 = 661
feet.
2. Because this map is on a computer screen, it is a little difficult to measure
horizontal distance accurately. Let's assume the distance is 2000 feet. So
2000 feet is your horizontal distance (sometimes called the "run").
So the gradient is (rise/run) 661'/2000' = 0.33 Which is commonly stated as 33%
Now it's your turn. Figure out the gradient of the ROAD from point "A" to point "B".
Once again because it may be a little tough to measure distance on the computer
screen (and I want everyone to come up with the EXACT same number) let's assume
the distance is exactly one mile.
Before you begin I need to tell you one last thing. When calculating gradient, the units
for rise and the units for run MUST BE THE SAME. So if you use feet for the rise, you
must also use feet for the run, which means you will need to convert 1 mile into feet (1
mile = 5280 ft).
So, what is the gradient of the road?
Streams and Stream Valleys
Streams are obvious features on topographic maps. They are represented by blue
lines. Stream valleys can be recognized by the pattern made by the contour lines
around the stream. Since streams are found in local topographic lows, the contour lines
double back on themselves forming a "V" shape pattern. Steam valleys often extend
farther than the steams shown on the map by blue lines, as can be seen by the contour
pattern.
Look at the map below of the Spruce Knob area. Where are the stream valleys? Scroll
down to find out.
The heavy blue lines on the map below show the locations of stream valleys. Notice
these lines are longer than the actual stream symbol on the map. The contour pattern
has been used to recognize the rest of the stream valley.
The blue lines outlining the streams on the map below have arrows showing which way
the stream is flowing. There are two ways to figure this out. First you can look at the
elevation of the contour lines that cross the stream. Water will always flow down hill so
the elevation of the contour lines will decrease in the direction water is flowing.
The second way to tell is to look at the pattern of the contour lines. Because streams
will sit in a valley, the land on either side of them will be higher. As a result the contour
lines form a "V" pattern like the one in the red circle on the map below. The point of the
"V" points up stream. The open end of the "V" faces downstream. It is the presence of
this "V" pattern that was used to recognize stream valleys where no stream was shown
on the map.
Notice that one stream has been marked with a broken blue line. There is no obvious
"V" pattern to the contour lines in this valley, but instead there is a broad curve in the
contours. There probably is not a single stream in this area, but water would flow down
slope in this general area until it reached a better defined stream channel.
Rules for Contour Lines:
1) Contour lines do not intersect one another (except in the rare case of an overhanging
cliff).
2) All contour lines are continuous or extend to the margin of the map.
3) Contour lines drawn across a stream form a V-shaped pattern with the V pointing
upstream.
4) Closed contours appearing on the map as ellipses or circles represent hills or knolls.
5) Closed contour with hachures (short lines pointed down slope) indicate closed
depressions.
6) Contour lines are labeled by multiples of the contour interval starting with zero, not
starting with a benchmark elevation. Example: If the contour interval = 50’ and a bench
mark elevation is 627’, the contour line above will be 650’ and the one below will be 600’,
not 687’ and 587’.
7) The last contour line crossed on one side of a ridge top or valley bottom is the first
contour line crossed on the opposite side.
8) Steep slopes are shown by closely spaced contours; gentle slopes by widely spaced
contours.
Scale: 1 inch = 1 mile
Contour Interval = 100 feet
1) Label the contour lines
2) The elevation of point A is greater than ________, but less than ________.
3) The elevation of point B is greater than ________, but less than ________.
4) The elevation of point C is greater than ________, but less than ________.
5) What is the approximate elevation of the lake surface in the southern portion of the map?
Practice Drawing Contours:
Scale: 1 inch = 1 mile
Contour Interval: 100 feet
Scale: 1 in = 2,000 ft
Contour Interval 100 feet
Draw contour lines for this map. Remember the rule of V’s!