Transcript LATITUDE AND LONGITUDE

Locations, Latitudes, Longitudes,
The Geographic Grid, Time Zones,
Map Projections
• Being able to convey (or communicate) where
things are, is essential to describing and
analyzing aspects of Physical Geography.
• A Map is essentially a communication device
• Communicates spatial data/information through
“graphic symbols” – a language of location
(Appendix B in Text)
Emergence of Cartography
– the art and science of mapmaking
– increasingly an automated, computerized process
 However, Maps and
Mapmaking have evolved
over the years, becoming
increasingly more complex,
sophisticated, automated, and
ubiquitous
 The challenge has always
been to represent locations
and patterns on earth
accurately and efficiently
Maps have been in existence since time immemorial
– simple maps of relative locations
Town Plan from Catal Hyük,
Anatolia, Turkey, 6200 B.C.
Reconstruction of Drawing

Clay tablets
from Ga-Sur
2500 B.C.
Interpretation
of drawing

The world according to Herodotus 450 BC

Reconstruction of world map according to Dicaearchus (300 B.C.)
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Early attempt to make locations more precise – Absolute Location
The first Lines
of Parallels
and Meridians
Eratosthenes
c276 - 195 B.C.
Earth’s Dimensions :
An Oblate Spheroid or Ellipsoid (Newton, 1687)
Lines of Parallel equate to Latitude
Latitude is measured from the Equator (00) to the Poles (900 N/S)
Lines of Meridians equate to Longitude
Longitude is measured from the Prime Meridian (00) to the
International Date Line (1800 E/W)
Both Latitudes and
Longitudes are
measured in angular
distance from the
center of the earth
Together, the Lines of Latitude and Longitude
constitute the Geographic Grid
Locating Los Angeles, California
Measuring Latitudes
(a)
Lines of Latitude –
measured in angular
degrees (°) from the
center of the earth,
North and South of the
Equator
Each Degree subdivided into
Minutes (′), and Seconds (″)
(b)
Lines of Latitude – parallel
and evenly spaced (hence,
Parallels of Latitude)
Special Parallels and Global Latitudinal Zones
Special Parallels: Equator (0◦), Tropic of Cancer (23 ½° N),
Tropic of Capricorn (23 ½° S), Arctic Circle (66 ½° N), and Antarctic
Circle (66 ½° S) → Latitudinal Zones
Measuring Longitudes
Lines of longitude or meridians – non-parallel circular arcs that
converge at the poles – measured in angular degrees (°) from the
center of the earth, East and West of the Prime Meridian
There are 180° of longitude on either side
of the Prime Meridian – which is 0°, and
starts at the Royal Observatory at
Greenwich, London
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A degree of latitude represents a constant distance on the ground -approx. 69 miles or 111 km – from the equator to the poles
At the equator, a degree of longitude measures about 69 miles (111
km), at 40° N or S, 53 miles (85 km), and at the poles, 0 miles (0 km)
Sextants and Chronometers – used to measure latitudes and
longitudes – now increasingly GPS
Equator is a
Great Circle:
dividing the earth
into two equal
halves
Earth’s Rotation and Time:
• Before 1884, “Local Time”
based on Solar Noon
• Now, we have Time Zones – Why?
• In 1884, International Meridian Conference
in Washington, D.C. established:
a) Prime Meridian (through Greenwich) – GMT and Universal
Time Coordinated (UTC) ↔ In 1972 became legal
official time in all countries
b) Time Zones – 24 Zones, 15 Degrees or 1 Hour apart,
7.5 Degrees East & West of the Central Meridian of the
respective zones
International Standard Time Zones
New World/North American Time Zones
 International Date Line: IDL
Established in the 1880s, and
it follows the 180° meridian,
with adjustments
 The International Date Line lies
directly opposite the prime
meridian, having a
longitude of 180°
 Crossing the line traveling east,
we turn our calendar back
a full day (i.e., gain a day);
Traveling west, we move
our calendar forward one
day (i.e., lose a day)
Latest Adjustment:
Samoa & Cook Islands
The challenge is to transfer a spherical grid (or the
Geographic Grid) onto a flat surface
Visualizing
the transfer
of a spherical
grid (or the
Geographic
Grid) onto a
flat surface
 Created by transferring points on the earth onto a
flat surface. Like having a light in the center of the
earth, shining through its surface, onto a projection
screen (or, projection surface)
 Projections now developed mathematically,
using computer algorithms
 There are three basic types of map projection:
(Based on the presumed positioning of projection surface)
1. Cylindrical
2. Planar (or Polar or Zenithal)
3. Conic (or Conical)
Point of contact at
equator
Note increasing distance between lines
of latitude….why?
Watch Video:
http://www.youtube.com/watch?v=AI36MWAH54s
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In a Mercator projection, lines of longitude are straight vertical lines
equidistance apart at all latitudes – so horizontal distances are
stretched above and below the equator – more toward the poles
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Mathematically stretches vertical distances by the same proportion
as the horizontal distances so that shape and direction are
preserved
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Preserves what sailors in the 16th century needed – shapes and
directions; they were willing to accept size distortion
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Any straight line drawn between two points on a
Mercator Projection represents a “rhumb line” – it
shows true compass direction
Mercator Projection was
the navigation map of
choice for sailing ships:
good direction, even
though longer route
Projection
centered on
the North Pole
◦ Great circles are
represented by
straight lines,
making it very
useful in plotting
Great Circle Routes
between selected
destinations
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Gnomonic Maps are
the navigational maps
for the “Air Age”
Gnomonic projections can be either “Conformal” or
“Equal Area”, but not both
A better choice for
mapping mid-latitude
regions such as the
United States is a
conic projection.
Locations near the
line(s) where the
cone is tangent to the
Earth, the standard
parallel(s), will be
relatively free of
distortion
 Distortion – It is impossible to flatten a spherical object without some
distortion in its basic attributes or properties
 Map Projections try to preserve one or more of the following properties:
 Area – relative representation of area size on map (for small areas).
Projections that preserve ‘area’ are “Equal Area” projections.
 Shape – when meridians (longitude) and parallels (latitude) are made to intersect
at right angles, shape is preserved locally.
Projections that preserve “shape” for small sections are “Conformal.”
 Direction – or “azimuthality” – maintain cardinal directions (N,S,E,W).
Projections that preserve “direction” are “Azimuthal.”
 Distance – variation in distance or scale on the same map ought to be minimized.
Projections that preserve “distance” are “Equidistant.”
 CONFORMAL vs. EQUAL AREA: Projections can be either
conformal or equal area – but not both!
Compromise Projections
The Robinson Projection is among the compromise projections that
uses tabular coordinates rather than mathematical formulas to make
earth features look the "right" size and shape.
A better balance of size and shape results in a more accurate picture of
high-latitude lands like Russia and Canada. Greenland is also truer to
size but compressed. It was adopted by the NGS in 1988.
http://www.youtube.com/watch?v=AI36MWAH54s
Compromise Projections
Watch Video: http://www.youtube.com/watch?v=AI36MWAH54s
– Interrupted Case