Topographic Maps
Lab 2
Concepts
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Map projections
Map scale
Topographic maps
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Contour lines
Topographic profiles
Basic map elements
“map”: a representation, usually on a flat
surface, of features on the earth showing
respective forms, sizes, and spatial
relationships
Map Projections
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Why “projections”?
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A globe is the only true representation of the Earth
Have many methods of transforming the 3D Earth’s
features onto a 2D flat surface
Flat maps cannot exist without a projection
Projections distort features in one of the following ways:
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Size
Shape
Direction
Distance
Map Projections: Mercator
Mercator made allowances in this projection and opted for true shape.
But size has suffered… look at Greenland on a globe, then this map.
Map Projections: Peters
Peters distorts shape but gives true size in his projection.
Compare Greenland from here to Mercator’s projection.
Mercator vs Peters – who is right?
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No single projection is ideal for all
purposes.
Depending on the use of your map, choose
the projection carefully.
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Learn more about projections here:
http://erg.usgs.gov/isb/pubs/MapProjections/projections.html
Map Scale
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Scale indicates how much
the Earth has been reduced
for reproduction on a map.
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Ratio of the image on a
map to its true size
Small vs Large scale maps
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“Small scale maps” show a
large area of Earth with less
detail.
“Large scale maps” show a
small area of Earth in great
detail.
Map Scale: 3 Methods
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Written/Verbal scale
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Representative Fraction (RF) scale
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States the ratio
“One inch equals five miles”
Shown as a ratio or fraction
1:24,000 or 1/24,000
No units provided. *You* apply the same unit of measurement
to both sides of the ratio, and it will be true.
1 inch [on the map] : 24,000 inches [on the Earth]
Graphic scale
Topographic Maps
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Older maps were 15-minute series
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Newer maps are 7.5-minute series
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15’ latitude x 15’ longitude
7.5’ = ¼ of the 15’ maps
Often called “quad”rangle maps
Standardized color scheme
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Brown – contours
Blue – water
Black – human-made features
Green – vegetation
Red – important human-made features
Pink – urban areas
Purple – revisions/updates due to aerial photos
Topographic Maps: Contours
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Topographic maps show the lay of the land
using isolines called “contours”
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Isoline = line connecting points of equal value
Contours connect points of equal elevation
A datum is a reference point from which all
elevations are measured.
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On topo maps, what do you think is the reference
point (“zero datum”)?
Topographic Maps: Contours
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Rules of Contour Lines
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Contours are drawn at regular intervals (e.g., every 10
feet of elevation). Called “Contour Interval.”
Contours are always closed loops, though they usually
travel beyond the margins of the map.
Contours never cross each other.
Where contours are close together, they show a rapid
change in elevation. Where they are far apart, they show
a gradual change.
Values inside a closed contour line are higher than
outside the contour line.
See other rules on page 59 of your lab manual.
Topographic Maps: Contours
CONTOUR INTERVAL
 Spacing between
each contour line
 This will be a
consistent number.
 Watch for the unit of
measurement
associated with the
contour interval.
INDEX CONTOUR
 Every 5th contour line
 Indicated by a heavier
line.
 Helps draw your eye
to certain intervals.
 Allows the mapmaker
to simplify the map –
may only label index
contours instead of
every line.
Topographic Maps: Contours
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The contour interval
is marked with a
specific unit of
measurement.
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You can see the
index contours
every five lines.
Contour Interval: 200 feet
Topographic Maps: Contours
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When reading a map, all points on a contour
line are the same elevation.
Otherwise, you must interpolate the point.
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e.g., “a” = 104 ft
e.g., “b” = 170 ft
e.g., “c” = 196 ft
Contour Interval = 20 feet
Topographic Maps: Contours
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Hill: represented by a
concentric series of closed
contours.
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Depression: indicated by
hachure marks on the
downhill side.
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Rule of Vs: Contour lines
“V” upstream when crossing
a stream. The point of the
“V” points uphill.
Topographic Maps: Contours
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Contours allow us to find the relief of the
landscape.
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Relief = difference in elevation between two points on a
map
Total/Local Relief = difference in elevation between the
highest and lowest points on a map
Topographic Maps: Profiles
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Topographic maps
show a birds-eye
view of the
landscape.
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Topographic
profiles show a
side-view of the
same landscape.
How to
Create
Profiles
Elevation (m)
How to
Create
Profiles
Elevation (m)
How to
Create
Profiles
Topographic Maps: Basic Elements
You should be able to
locate the following:
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Map Body
Title
Location
Date
Data sources
Direction
Legend
Projection
Scale