Latitude and Longitude
• Latitude
– Angular distance in °
between center of the
earth and a point on
the earth’s surface
• parallels
• Longitude
– Angular distance in °
east or west of a point
on the Earth’s surface
• meridians
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LAT AND LONG
• LATITUDE- MEASURES N AND S OF
EQUATOR (0 TO 90°) BUT RUNS E AND
W
• LONGITUDE MEASURES E AND W OF
PRIME MERIDIAN (O TO 180°) BUT
RUNS N AND S
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LATITUDE AND LONGITUDE
30°N
EQUATOR
0°
NEW ORLEANS
30°N 90°W
90° W
0°
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Lat and Long Distances
• Latitude
– 69.13 miles (111.23 km) between each degree
of latitude
• Longitude
– Varies by latitude
• 69 miles at equator only
• 59.9 miles at 30°
• 34.6 miles at 60°
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Lat and Long estimation
• Latitude
– Can be estimated using the north star
(Polaris), or Southern Cross
• Longitude
– Very tricky
• 1700’s difference between fixed clock and ship
clock
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TIME ZONES
• International Date Line
– SEPARATES ONE DAY
FROM THE NEXT
• WHERE THE NEW DAY
STARTS
• Earth’s rotational speed is
approximately 15°
longitude/hour
• So 24 time zones
• ANY LOCATION EAST OF
OUR TIME ZONE UP TO 180°
E IS AHEAD OF US
• ANY LOCATION WEST OF
US UP TO THE DATE LINE
(180°) IS BEHIND US
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Time Zones
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Keeping Time
• UTC or Z time
– London 5 hours ahead
– 6 on ST
• DST
• New DST
– Not in Arizona, Hawaii
• Indiana?
– Now observes DST
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Map Projections
• Graticule → flat sheet
of paper
– 3D to 2D
– distortion in 4 main
properties
• major – pertains to all
areas
– conformality (shape)
– equivalence (area &
scale)
• minor – pertains to only
1 or 2 points
– equidistant (distance)
– azimuthal (direction)
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Shape vs Area
• Conformality (shape)
– retention of correct
angles
– requirements
• meridians & parallels
cross at right angles
– misleading
• small areas VS large
areas
• Equivalence (area) is lost
• Equivalence (area)
– unit area on map =
same square unit on
globe surface
– characteristics
• right angle crossing is
lost
• shape distorted
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Minor Properties
• Equidistant (distance)
– measure from center
• others area are incorrect (significant amount)
• equivalence (area) is lost
• DO NOT measure distance on a map
showing a large area unless it is
equidistant
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Minor Properties and Other
• Azimuthal (direction)
– true directions from 1 central point
• others inaccurate
• can preserve 1 other property
• Other
– Compromise
• does not preserve any of the 4 main properties
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Map Projections
• 4 general classes
– planar (azimuthal)
– cylindrical
– Conic
– oval
– and miscellaneous
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Planar Projections (Azimuthal)
• Flat sheet of paper
– @ pole – polar aspect (simplest);
• least distortion
– @ mid-latitude – oblique aspect;
– @ equator – equatorial aspect
• Azimuthal projection
– air navigational
– hemispheres
• No (minimal) modifications
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Lambert Azimuthal Equal Area
• Map large ocean areas
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Oblique Aspect Orthographic Projection
• Perspective views of hemispheres.
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Cylindrical Projections
• Tangent to line(s) on sphere
– normal @ equator
• Characteristics
– meridians do not converge at poles
– space parallels further apart
– smaller area – shape preserved
• Uses
– atlases
– map of the world
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Behrmann Cylindrical Equal-Area
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Peters Projection
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Mercator Projection
• Marine navigation
– rhumb line
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Miller Cylindrical Projection
• Avoids scale exaggerations of the Mercator
– shape & area distorted
– true direction along equator
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Conic Projections
• Cone enveloped around sphere
– normal – cone is tangent along a
chosen parallel
• Area and shape preserved
• Simple Conic & Polyconic
• Uses:
– areas w/ east-west extent
– National Atlas of the United States
of America
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Conic
Polyconic
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Albers Equal Area Conic
SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
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Miscellaneous Projections
• Unprojected Maps
– distortion
•
•
•
•
scale,
distance,
area, &
shape
– increases toward the poles
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
World: Unprojected
Latitude and Longitude
N. America: Unprojected
Latitude and Longitude
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SOURCE: Peter H. Dana, Department of Geography, University of Texas at Austin, 1995
Choosing a Map Projection
• 1st step is to determine:
– location
– size
– shape
• These 3 determine where the area to be
mapped falls in relation to the projections
distortion
– country in the tropics – cylindrical projection
– country in the temperate zone – conical projection
– polar area – planar projection
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Choosing a Map Projection (2)
• These global zones map into the areas in each
projection where distortion is lowest:
– Cylindricals are true at the equator and distortion
increases toward the poles.
– Conics are true along some parallel somewhere
between the equator and a pole and distortion
increases away from this standard.
– Planar are true only at their center point, but generally
distortion is worst at the edge of the map.
• Can make other modifications
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