Topographic Maps
8.9C Interpret topographical maps and satellite views to identify land and erosional
features and predict how these shapes may be reshaped by weathering
What are some ways to represent Earth’s
surface?
▪ Maps are models that represent Earth’s surface.
▪ They are helpful because they can show large areas of
the three dimensional surface on small, flat surfaces.
▪ Different types of maps show different types of
information.
▪ Latitude and longitude are used to find places on
Earth
▪ All flat maps distort Earth’s surface
Globe:
▪ A round map!
Here is the same information – flat!
▪
Not very readable is it?
Because the Earth is round and maps are flat, it is impossible to create a map with a
perfect scale. Some parts of the map will be too large, while others will be too small. The
larger a territory represented by a map, the greater that the distortions in scale will be.
Aerial and Satellite Images
▪ Aerial means taken from airplanes and satellite means from
satellites that orbit Earth
▪ Some look like photographs and some are a collection of data
that may not be visible (such as infrared that looks at
temperatures on earth)
More on Satellite Views
▪ Satellite views can be used to learn about erosion and how the land has
changed
▪ images taken over time can be used for comparison and interpretation
of erosional features (ex. after a flood)
Geological Maps
▪ Geologic maps shows rock types
and ages
▪ They also show geological
features and fault lines
▪ Colors and letters give
information about the rocks,
while lines show elevation
Key Features
on Maps:
▪ Map title
▪ Compass
rose/orientation
▪ Map key or legend
▪ Map scale
▪ Location markers
(latitude and
longitude)
What’s the
difference?
What are the uses of topography in the real world?
Topography has a number of uses including:
▪ Agriculture - Topography is often used in agriculture to determine how soil can be
conserved and how water will flow over the land.
▪ Environment - Data from topography can help to conserve the environment. By
understanding the contour of the land, scientists can determine how water and wind
may cause erosion. They can help to establish conservation areas such as watersheds
and wind blocks.
▪ Weather - The topography of the land can have an impact on weather patterns.
Meteorologists use information on mountains, valleys, oceans, and lakes to help
predict the weather.
▪ Military - Topography is also important to the military. Armies throughout history
have used information on elevation, hills, water, and other landforms when planning
their military strategy.
Texas
▪ Historically, mapmakers
used a variety of
methods to indicate
elevation. To get a quick
sense of elevation, we
can use color, as in this
map.
Contours and Profiles
You can generate a profile of a landform from the contour lines on a
topographic map. But you probably don’t have access to this
technology – so what do you do on a trip?
Simple contour map
▪ Imagine you are on vacation with your family in a national park.
You have a simple trail map that shows you where to hike. But
the map does not tell you anything about what the land looks
like. Will you have to cross any rivers or valleys? How far uphill or
downhill will you have to hike?
So on your vacation you need - Topographic Maps!
▪ Topography is the shape, or
features, of the land.
▪ These features can be natural—
such as mountains, plateaus, and
plains—or human-made—such as
dams and roads.
▪ To show the topography of an area,
mapmakers draw a topographic
map.
On vacation you would need a topographic map!
▪ People use topographic maps to
locate interesting landforms, to
find their way through an area,
and to determine the direction
water flows in an area.
▪ The wiggly lines are called contour
lines. They show elevation, slope
and relief
Elevation, slope and relief:
▪ Elevation – how high above sea level
a place is
▪ Slope – how steep it is. The more
gradual a slope, the further apart the
contour lines are, the steeper, the
closer the lines
▪ Relief – the difference between its
high and low points.
▪ For example, subtracting the lowest
elevation on a map from the highest,
gives you the measure of the area’s
relief
Elevation, slope and relief on a map:
A closer look at Contour Lines
Equal
elevation
Follow any given line from
one side to the other.
This continuous line
indicates equal elevation.
http://www.4orienteering.com
Rules of Contour Lines
▪ Never cross each other
▪ Connect with themselves
▪ The contour interval is the same on a map
▪ Get closer together as land gets steeper
▪ Get further apart as land gets flatter
▪ Circles show highest and lowest points
(tops of mountains and bottom of
depressions)
Contour Interval
The change in elevation from contour line to
contour line is called the contour interval
The
distance
that
separates
contour
intervals
How do they make topo maps?
▪ There are a number of ways that information is
gathered to make topographical maps. They can
be divided into two primary methods: direct
survey and indirect survey.
▪ Direct survey - A direct survey is when a person
on the ground uses surveying equipment, such as
levels and clinometers, to directly measure the
location and elevation of the land.
▪ Indirect survey - Remote areas may be mapped
using indirect methods. These methods include
satellite pictures, images taken from planes,
radar, and sonar (underwater).
Learning to read topo maps
▪ Learning to use a topographic map is a
difficult skill, because it requires you to
visualize a three-dimensional surface
from a flat piece of paper.
▪ Land Features and other objects are
also indicated on a topo map
▪ More examples and links are posted on
my website: Unit 4
Land Features you may see on a Topo Map:
Land Feature - Hill
A small area of high ground. When you are on a hill, the
ground slopes down in all directions.
Land Features - Depression
Depression-a low point or hole in the ground, surrounded on all sides by higher ground.
Land Feature - Saddle
▪ Saddle-a dip or low point along the crest of a ridge. A saddle is not necessarily the
lower ground between two hilltops; it may be a break along an otherwise level ridge
crest.
Land Feature - Cliff
▪ Cliff-a vertical or near-vertical slope. A cliff may be shown on a map by contour lines
being close together, touching, or by a ticked "carrying" contour line. The ticks
always point toward lower ground.
Grand Canyon – Isis Temple – Can you find the cliffs?
Land Feature - Valley
Valley-reasonably level ground bordered on the sides by higher ground. A valley may
or may not contain a stream course. A valley generally has maneuver room within its
confines. Contour lines indicating a valley are U- shaped.
Land feature - Ridge
Ridge-a line of high ground with height variations along its crest. The ridge is not
simply a line of hills; all points of the ridge crest are higher than the ground on both
sides of the ridge.
Tracking Flowing Water
▪How does water always flow?
DOWNHILL
▪How can we tell what direction (ex.
N,S,NW,ESE) is downhill?
PSC 121 Prince
George's
Community
Tracking Flowing Water (streams)
You can look for elevation
changes since water will
flow from higher to lower
elevations.
Water will always flow down
hill so the elevation of the
contour lines will decrease
in the direction water is
flowing.
Here the stream flows toward
the northwest.
2000 ft
2100 ft
Second way to read a stream:
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
on the map
Downstream
PSC 121 PRINCE GEORGE'S COMMUNITY COLLEGE
Upstream
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 erosion may occur
▪ A stream would run down the middle or side of the V’s – this is the most
likely place where erosion would occur.
▪ Over time, this could change the landscape, erosion causes steep
grades to “soften”. This is shown by the spaces in between contour
lines getting wider.
Reminder of key terms!
▪ Weathering – is the
breaking down of rocks, soil
and minerals
▪ Erosion – a process (such as
water flow or wind) which
removes soil and rock from
one location on the Earth's
crust, then moves it
▪ Deposition – the location
where freshly eroded
material gets placed
How can flowing water shape land?
▪ By weathering and eroding material – Land gets weathered and eroded by flowing
water. These, over time, form features such as valleys, cliff and canyons.
▪ Streams carry small pieces of sediment, while larger rivers carry larger particles and
major storms can carry even larger pieces, like boulders.
▪ Groundwater below the Earth’s surface form caves and this dissolved material is then
eroded and the groundwater flows to new locations.
▪ Deposition by flowing water makes alluvial fans and deltas – which help make flatter
landscapes.
▪ Heavy rainfall and floods can cause rivers to rise and bring sediment to higher places
▪ Glaciers are also factor and can carve away entire mountains, or they may form lakes
when they recede or melt.
Let’s see what you have learned.
E
C
D
B
1200m
A
F
1000m
800m
600m
1. Could the elevation at the peak (B) be 1410 meters?
No :The elevation must be under 1400
meters, but over 1300 meters.
E
C
D
B
1200m
A
F
1000m
800m
600m
2. What is the elevation at (E)?
About 400 meters
E
C
D
B
1200m
A
F
1000m
800m
600m
3. If you walked a straight line from (D) to (C) would
you walk over a ridge or down a valley?
Down a valley: If the contour lines point up the slope
it’s a valley, if they point down the slope it’s a ridge.
E
C
D
B
1200m
A
F
1000m
800m
600m
4. Just looking at the map, would it be easier to head down from the
peak going East, or going North?
East: When contour lines are close together that means there is a steep slope, the
further apart the lines, the more gentle N
the slope and therefore an easier walk! Go
east!
E
C
W
D
B
E
1200m
F
1000m
A
800m
600m
S
Contour Practice
1.What is the contour interval of the map at left? How do you
figure this out? 80 m
1.What is the elevation of point A?
320 m
2.What is the elevation of point B?
880 m
3.What is the elevation change between A and B?
560 m
Map Reading Activity: Topography Practice
Map your hand!
Supplies:
1. Your hand
2. Marker
Close to Home
▪ Local maps
▪ http://www.topozone.com/states/Texas.asp?county=Bexar
▪ http://www.trails.com/topo.aspx?lat=30.50639&lon=98.81861&s=50&name=Enchanted%20Rock
▪ Topo Map - http://www.youtube.com/watch?v=EqyfJMgFL-U