Representations of Locations and Patterns
Topics of Discussion
The physical effects of rotation
The geographical use of rotation
Latitude and longitude
The geographic grid
Global time
Map Projections
The Geographical Use of Rotation
Earth's rotation provides a reference system for location.
The earth rotates around two fixed points:
• North Pole
• South Pole
Rotation and Latitude
Halfway between the poles, the equator divides the earth
into two equal hemispheres.
Lines north and south of the equator are parallels.
Parallels are lines of latitude.
Latitude is measured at an angle from the center of the earth,
north and south of the equator.
The first Lines
of Parallels and
Meridians
Eratosthenes
270 - 195 B.C.
LATITUDE AND LONGITUDE
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
MEASURING LATITUDE
• The Equator is a Great Circle: dividing the earth into
two equal halves
• The Lines of Latitude are measured in angular degrees
(°) from the center of the earth, North and South of the
Equator
• Lines of Latitude are parallel and evenly spaced (hence,
Parallels of Latitude): a degree of latitude represents a
constant distance on the ground -- Approximately 69
miles (111 km)
• Special Parallels: Tropic of Cancer (23 1/2° N),
Tropic of Capricorn (23 1/2° S), Arctic Circle (66 1/2°
N), and Antarctic Circle (66 1/2° S)
Locating Los Angeles, California
Meridians or Longitude
Lines drawn from pole to pole are called meridians or
lines of longitude.
Longitude measures points east and west of the Prime
Meridian.
The prime meridian passes through Greenwich, England.
MEASURING LONGITUDE
• Lines of longitude or meridians are non-parallel circular
arcs that converge at the poles
• At the equator, a degree of longitude measures about 69
miles (111 km), at 400 N or S, 53 miles (85 km), and at
the poles, 0 miles (0 km)
• There are 180° of longitude on either side of the Prime
Meridian – which is 0°, and starts at the Royal
Observatory at Greenwich, London
• Each Degree of Latitude and Longitude is subdivided
into Minutes (’), and Seconds (”)
• Sextants, and Chronometers are used to measure
latitudes and longitudes – now increasingly GPS
Together, the Lines of Latitude and Longitude
constitute the Geographic Grid
Geographic Grid
Together, latitude and longitude form a
geographic grid.
Latitude and longitude can be used to define
precise locations on earth.
Absolute Location
The absolute location of San Francisco is latitude
37º 45"N and longitude 122º 26"W.
Rotation
Earth rotates on its imaginary axis like a top.
The earth rotates from west to east.
Each rotation defines a solar day - 24 hours.
What are the physical affects of earth’s rotation?
1.Daily Cycle of Night and Day
Longitude, 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) or Zulu Time
b) Time Zones – 24 Zones, 15 Degrees or 1 Hour apart,
7.5 Degrees East & West of the Central Meridian of
respective zones (Figure 2.9)
Global Time
What time is it on earth?
Global time is Solar time
Solar noon - the sun’s highest point in the sky
Standard time is a device to improve global timekeeping.

The world is divided into 24 time zones.
Each time zone is based upon standard meridians at 15°
intervals from the prime meridian.
International Date Line
The International Date Line is the 180º meridian.
Crossing the date line requires adjusting your
calendar as well as your watch.
You lose a day going west and gain a day going
east.
 International Date Line:
IDL was also established in
the 1880s, and it follows the
180 degree meridian, with
adjustments (Figure 2.10)
 The International Date Line lies
directly opposite the prime
meridian, having a
longitude of 180º
 Crossing the line traveling east
one turns their calendar
back a full day; Traveling
west one moves their
calendar forward one day
How do you Represent Locations,
Places and Patterns of Earth?
• 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)
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
Very Early Map
Town Plan from Catal Hyük,
Anatolia, Turkey, 6200 B.C.
Early World Maps
• The world according to Herodotus 450 BC
Early World Map
•
Reconstruction of world map according to Dicaearchus (300 B.C.)
•
Early attempt to make locations more precise – Absolute Location
Map Projections
The challenge is to transfer a spherical grid (or the
Geographic Grid) onto a flat surface
Maps and Projections
1.Geographers and other disciplines use a variety of tools that
help describe the cultural and physical features on the Earth's
surface.
2. A globe shows the earth in 3D.
3.A map is a two-dimensional representation.
4.The science of map making is Cartography.
5.Maps can be two general types: reference maps and thematic
maps.
6. Reference maps show basic locational information such as
roads, cities, and rivers. Examples include topographic maps
and Google maps.
1.Thematic maps show the distribution of specific geographical
information such as weather map or population.
Projections – Going from a Sphere
to Flat Maps
 Projections are created by transferring points on the
earth onto a flat surface. It is like having a light in the
center of the earth, shining through the earth’s surface,
onto the projection surface
 There are three basic methods for doing this:
 Cylindrical – projection surface wrapped around the Earth; point
of contact is equator
 Planar – (or Polar or Zenithal) – projection surface is a ‘flat’
surface against the Earth at a particular latitude or longitude
 Conic (or Conical) – projection surface is a cone is placed on or
through the surface of the Earth – Where the projection surface
touches the earth is the “Standard Line” or “Standard Parallel”
 Projections now developed mathematically, using computers
Projection Challenges
 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 – usually referred to as “conformality”, again for small sections
Projections that preserve “shape” are “Conformal”
 Direction – or “azimuthality” – cardinal directions (N,S,E,W)
Projections that preserve “direction” are “Azimuthal”
 Distance – variation in distance or scale on the same map
Projections that preserve “distance” are “Equidistant”
 CONFORMAL vs. EQUAL AREA: Projections can be either conformal or
area – but not both!
equal
Projections – Cylindrical Projection
Point of contact at
equator
Cylindrical Projection:
Mercator – A Conformal Projection
Note increasing distance between lines
of latitude….why?
Why Mercator? NAVIGATION!
• In a Mercator projection, the lines of longitude are straight vertical
lines equidistance apart at all latitudes, and horizontal distances are
stretched above and below the equator – more toward the poles
• The Mercator projection mathematically stretches vertical distances
by the same proportion as the horizontal distances so that shape
and direction are preserved
• Mercator’s projection preserves what sailors in the 16th century
needed – shapes and directions; they were willing to accept size
distortion
• Any straight line drawn between two points on a
Mercator Projection represents a “rhumb line” – true
compass direction
True Compass
Heading: Rhumb
Line in Mercator
Projection
Mercator Projection was
the navigation map of
choice for sailing ships:
good direction, even
though longer route
Projections — Polar/Planar Projection
Polar/Planar Projection
Projection
centered on
the North Pole
Polar Navigation?: GNOMONIC!
• Any straight line drawn on
a gnomonic projection is
an Arc of a Great Circle
Route
– Great circles are
represented by straight
lines, making it very useful
in plotting Great Circle
Routes between selected
destinations
• Gnomonic Maps are the
navigational maps for the
“Air Age”
Gnomonic projections can be either “Conformal” or
“Equal Area”, but not both
Projections — Conic Projection
Conic Conformal Projection
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
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 – Interrupted
Watch Video: http://www.youtube.com/watch?v=AI36MWAH54s
MAP SCALE
• Map scale is the ratio of the distance between two
points on the Earth’s surface and the distance
between corresponding points on a map
• There are several types of map scales:
• Verbal Scale: 1 inch = 1 mile
• Bar Scale: a graph depicting distances
• Representative Fraction:
One unit of measured distance on a map equal some units of measured
distance in the real world – 1: 63360
LARGE-SCALE vs. SMALL-SCALE
• Large-Scale Maps show very small portions of the real
world, but with great detail
– Large-Scale maps have small denominators i.e.,
1:12,000 or 1:24,000
– Topographic maps are examples of large-scale maps
• Small-Scale maps show very large portions of the real
world, but with minimal detail
– Small-scale maps have large denominators, i.e.,
1:100,000 or 1:1,000,000
– Wall maps are examples of small-scale maps
LARGE -SCALE TO SMALL -SCALE
LARGE SCALE
SMALL SCALE
Ethnicity Map – Former Soviet Union
Choropleth Map with nominal data
• Special Purpose/ Thematic Maps:
 Composite Map – shows discrete + continuous data
(+ proportionate circles)