Mapping the Earth
Objectives
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Differentiate between planimetric and hypsometric maps
List and recognize the ways in which 3 dimensions can be portrayed on a paper (2
dimensional) map.
Define/describe map projections
Identify common projection shapes
Define/describe an undevelopable surface
Identify where distortion is minimized and maximized in a projection
Describe why a Mercator projection distorts area towards the poles.
Define/describe: cartographic scale, ecological scale, grain, extent, representative fraction
Explain why maps are models
Explain the differences between a large and small cartographic scale in terms of detail
and surface area represented.
Match locations according to their latitude and longitude
State the latitude and longitude for Lexington
State the latitude and longitude for the Tropics of Cancer, Capricorn and for the Arctic and
Antarctic circles.
Explain how time zones are designed
Explain UTC time
Describe the difference between geographic and magnetic north
Activities
• Make a map catalog showing the following types of
maps:
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Topographic
Bathymetric
Isohyets
Isopachs
Isotachs
Isobars
Geopotential heights
Cylindrical projection map
Conic projection map
Planar projection map
What is a map?
• A map is a model used to convey
patterns of physical or human
processes and patterns
• Maps are idealized representations of
reality.
• General map formats:
– Mental or cognitive maps
– Hardcopy (paper) maps
– Virtual (digital code) maps
Mental maps
Paper maps
Digital maps
Digital maps
Map information
• Planimetric
– Two-dimensional information
• Hypsometric
– Two dimensions plus a third dimension
– Third dimension is typically relief or
topography
– Ways of depicting relief
• Shading
• Contour lines
9. Maps invoke
symbolism
Uphill
direction
Rapid change
in elevation.
Contour lines
close together.
Slow change
in elevation.
Contour lines
far apart.
The contour interval is 20 ft.
Point elevations are:
A = 700 ft
B = 740 ft
C = 770 ft
D = 820 ft
Types of contour maps
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Topographic (terrestrial elevation)
Bathymetric (sea floor elevation)
Isohyets (rainfall)
Isopachs (rock or sediment thickness)
Isotachs (wind speed)
Isobars (air pressure)
Geopotential heights (altitude of a given
air pressure)
Topographic
map
Match the letter and number
Bathymetric maps (ocean floor relief)
Isobaric maps (air pressure)
Individual lines
are called
isobars.
Isobars (solid yellow
lines)
This is a strong low pressure
system, which produced large
amounts of snow and wind across
the eastern US.
In an isobaric map, where isolines
are close together, winds are the
strongest. Winds are strongest in
Virginia, North Carolina,
and West Virginia.
Isohyets(precipitation)
Isotach (wind speed)
Colored areas represent isotachs, lines encompassing areas of equal windspeed. Contour interval = 10 knots
Green lines are geopotential heights, the altitude at which one reaches 300 mb in air pressure. For example, 9720
represents 9720 meters. 300 mb in air pressure is reached when altitude is 9720 meters or about 32,000 ft.
Geopotential height maps (constant
pressure surface)
Geopoential heights
The blue lines are
geopotential heights. Contour
interval is 60 meters
How high would you have to
go up to reach 300 mb over
Kentucky?
Note that the wind barbs in
this map convey the direction
of wind flow.
Isopach map (contour interval = 5 ft) show the thickness of rock layers or some
subsurface feature. In this map they show the thickness of a rock layer known to
produce oil. The round symbols are oil well locations and the depths (6000 – 7000
ft) drilled to reach oil. Why would oil drillers want to know the thickness of an oilbearing rock layer?
Isopach map showing
thickness of the limestone
comprising the Florida
Aquifer
Isopach map showing
thickness of hydrocarbonbearing strata in western
Kentucky.
Map projections
• A projection is any number of
cartographic models used to project the
Earth’s curved surface as a flat surface
Why don’t we just use a globe
instead of flat maps?
• Globes are virtually
ideal models of the
world:
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Correct shape
Correct area
Correct distances
Correct direction
Because, globes are:
• Impractical
• Expensive to manufacture
• Difficult to plot routes on a
curved surface
• Users are overhead of a
single point (perspective
view), not an orthographic
view (directly overhead of all
points)
• Instead, we use:
Map projections
What are the tradeoffs for
projecting the globe onto a map?
• A sphere is an undevelopable surface.
An undevelopable surface cannot be
flattened into two dimensions without
some distortion.
Types of projections
Cylindrical projection
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Conic projection
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Planar projection
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Distortion from projection
• Every map projection distorts at least
three and sometimes all four, of the
following properties: shape, area,
distance, and direction
• No projected maps can have both true
shape (conformality) and true area
(equivalence).
distortion
ellipses
The Mercator projection
distorts area (look at Greenland),
but shape is true
Conformal (true shape) map
projection
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Equivalent (true area) map projection
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Cartographic scale
Cartographic scale
• Map scale is the ratio of the size of an object on
a map to its actual size
• Map scale is expressed with a representative
fraction (RF):
– 1:50,000
– 1:10,000
• These can be interpreted as: 1 inch = 10,000
inch or 1 cm = 10,000 cm. Any unit can be used
so long as they are on both sides of the equation.
Cartographic scale
• Assuming that you have two maps of the same
paper size, which of the two RFs shows the most
detail and the smaller surface area?
1:50,000
1:10,000
Impact of cartographic scale on
representation of data
1:250,000
1:50,000
1:2,500
Operational scale
Spatial and
temporal dimension
of an object or process
Ecological scale
Scale at which
observations and
measurements take
place
The geographic grid
Parallels run EW
but are measured NS.
Meridian run NS but are
measured EW
Meridians (lines of
longitude) converge at
poles
The distance spanned by
a degree of longitude
varies enormously
between the Equator and
the poles.
True north vs magnetic north
Magnetic declination: the
difference in angle between a
magnetic pole and a
geographic pole (true north).
Arctic Circle: 66.5 degrees N
Antarctic Circle: 66.5 degrees S
Tropic of Cancer: 23.5 degrees N
Tropic of Capricorn: 23.5 degrees S
Time zones (24 hours divided by 360 degrees equals 15
degree span for each time zone).
UTC time – Coordinated Universal
Time
Calculating UTC time from
LST in Lexington
• From March 13 to Nov 6 2016
– This is during daylight savings time, when
we have set our clocks ahead one hour to
take advantage of the longer hours of
daylight
UTC = LST minus 4 hours
• From Nov 6 up until March 13, 2016
– We set our clocks behind one hour
UTC = LST minus 5 hours
Practice
• On Sept 3 (2016) if it is 10 am on the
prime meridian (10Z), then it is 6 am
here in Lexington.
• On Dec 3 (2016) if it is 10 am on the
prime meridian (10Z) then it is 5 am in
Lexington.
• Today, Jan 26, at 18Z is ____ in LST
1/23/16 00UTC 048 HR FCST VALID MON 1/25/16 00 UTC NCEP/NWS/NOAA
When was this forecast model made in local
Lexington time/day/date? When is this
prediction valid in local Lexington time/day/date
Match the
locations with
their lat and
long:
Romford, England
Ropsha, Russia
Rosales, Mexico
Rosetown, Canada
51" 35' N
0" 11' E
59" 44' N 29" 53‘ E
28" 15' N 100" 43' W
51" 33' N 108" 00' W
What is the latitude and longitude for Lexington in
minutes and degrees?