Topographic Maps
Notes Packet
Introduction:
Topographic Maps are important tools of the Earth scientist. Many features are shown on the map by the use of
CONTOUR lines. A contour line is a line that connects points of l
elevation. The starting
point (0 foot contour line) is sea level. On the topographic map these lines are shown as
lines
In general, note how the contour lines are sub – parallel, they never
and they never split.
Notice also that every 5th line is a heavier line. These are called
and they are
emphasized on the map to make the counting of contour lines easier. For example the index contour directly
above the 2000 line is
.
How can you tell? You have to find out what the
important information is located at the bottom center of the map.
is. This bit of
Now that you understand that the normal contour lines are separated 20 feet from the lines above it and below
it, it makes sense that every 5th line is
feet difference in elevation. To make it easier to count
these lines the 5th line is darkened. These are the
lines.
Check out the position of the 1700 foot line.
What is the elevation of the little unnamed hill just above it on the right side of this illustration?
.
What is the elevation of the little unnamed hill just above it?
Remember the purple line is the
1700 foot line.
Going up to the summit (blue dot) of the hill, the next INDEX CONTOUR line is the 1800 foot line (red line).
Finally, there is one more index contour line closer to the summit. This is the 1900 foot contour line (black)
BUT, we are not yet quite to the summit. There are 3 normal contour lines. The next contour line would be the
1920, the next is the
and the one closest to the summit is the
.
So, the summit of this hill is a little over
another contour line.
feet. But it is below 1980 – otherwise there would be
While your looking at Squaw Peak, notice that the brown contour lines have different spacing. Where the
contour lines are close together, there is a
slope. Where the contour lines are farther
apart, the slope is more
.
One last thing about contour lines is that they “V” upstream when they cross a river drainage. Check out one of
the many unnamed streams on the map below. Blue represents water features on topographic maps, and the line
and three dot pattern of the streams on this map indicate an
stream – sometimes it flows and
sometimes it doesn’t.
Next, notice how the contour lines form a “V” and that the “V” points towards the
of Squaw
Peak (higher elevation), The rule of thumb is that the “V’s” point
,
There are even other drainages that are not marked by streams but simply by the pattern of the “V”s.
In this illustration of North Mountain Park (top central area of map) all the stream drainages will be highlighted
in purple. It includes the blue stream lines as well as the unmarked drainage. Before you advance to the next
image see if you can visualize where this additional drainage would be on just the west side of the mountain.
What was done was to draw a line that connects the tips of the “V”s. As you can see, this is a good example of
dendritic (
) drainage.
The top scale is called the
Scale 1: 24000.
scale:
This simply means that an inch on the map is equivalent to
inches on the surface of the
Earth. OR 1mm on the map is equivalent to 24000 mm on the Earth’s surface.
This is the graphical scale. The one you will be using in the lab is the mile scale (the top of the three scales).
Note that the total length of the scale is
miles.
The left side of the scale is divided into
and the right side is one mile. It is very important to note
the zero in the middle. It could make a huge difference in your measurements and thus the accuracy of your
answers.
Some Basic Information about Topographic Maps
COLORS:
BLACK – Artificial features like buildings, dams, trails, railroad lines
BLUE – Water bodies or glaciers
BROWN – Contour lines
GREEN – Vegetation
RED – Some main roads, fences, public land system revisions
PINK – Urban areas
PURPLE - Revisions