Topographic Maps
What is a Topographic Map?
Topographic maps are special maps
that show the relief (highs and lows) of
Earth’s surface.
Topographic maps are different from
regular maps because they use
isolines in addition to everything else.
What is an Isoline?
Isolines are lines that connect equal values.
The values are different depending on the map
being used.
Types of Isolines:
Isotherms – connect equal points of temperature
Isobars – connect equal points of air pressure
Contour lines – connect equal points of elevation
Contour Lines
For topographic maps, contour lines are the type of
isoline used to show equal points of elevation.
They look like the background of this powerpoint
presentation!
Contour lines show three different things on topographic
maps:
Elevation of the land
Shape of the land
Steepness of the slopes
Contour Lines
Contour lines look like this:
-All the points on the 200
line equal 200 meters, all
along the 300 equal 300
meters, etc.
- We know the elevation is
in meters because it tells us
at the bottom of the map.
Elevations in meters
-By using contour lines, we
can take a real-life, 3dimensional hill and draw it
on a flat, 2-dimensional
map!!!
Topo Map Link
Reading Contour Lines
The contour interval is the amount between each
line.
The contour interval in this map is 100 meters
since each line goes up by 100.
Reading Contour Lines
Usually, not every line is labeled for you. It will
either tell you the contour interval at the bottom
of the map, or you will have to figure it out.
50
100
300
150
250
200
Contour Interval = 100 m
Reading Contour Lines
The closer the contour lines are to each other,
the steeper the hill.
The further away the contour lines are from
each other the more gentle the hill.
GENTLE!!
STEEP!!
Reading Contour Lines
Each line goes UP by the contour interval unless it is a
hatchured contour. Those indicate depressions (holes).
The first hatchured contour after a regular is the SAME
value as the one that came before it, then each one
after that goes DOWN by the contour interval.
Then the first regular contour after a hatchured is the
same as the hatchured before it and then they go UP by
the contour interval after that.
Estimating Elevations
If a point is right on a contour line, you definitely
know it’s elevation. But, if it’s in-between 2
contour lines, you must estimate.
B
We know for sure point B
is 200 m because it’s
right on the 200 m
contour line.
We don’t know point A’s
elevation for sure though.
It’s probably about 350 m
Other Contour Line Rules
Contour lines NEVER cross each
other!
Contour lines NEVER split!
Contour lines MUST begin and end at
the edge of the map…cannot start or
end them in the middle of the map.
Drawing Contour Lines
You must ALWAYS connect points of equal
value!! Kind of like connect the dots when you
were little!
The lines you draw should be gentle, curving
lines, no sharp angles or edges.
CORRECT!!!
5
5
10
10
10
10
15
15
NOT CORRECT!!!
5
5
10
10
10
10
15
15
Gradient
Gradient is the average slope of a particular area
on a map.
You can calculate gradient for any map that has
isolines.
Formula:
Change in field value
Distance
Formula is on page 1 of ESRT!!!
Gradient
The field value is whatever the map is
measuring.
If it’s a topo map, it’s elevation.
If it’s a weather map it’s probably air pressure
(isobars) or temperature (isotherms).
The distance is just the distance found between
the 2 points given using the map scale.
Example
Gradient = change in field value
Distance
B
Gradient = 350 m – 200 m
2.3 miles
Gradient = 150 m
2.3 miles
Gradient = 65.2 meters/mile
Elevation in meters
0
.5
1
2 miles