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## Cartography: the science of map making

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### ... the earth in half and each half is known as a hemisphere. 2) are the circumference of the earth. 3) provide the shortest routes of travel on the earth's surface. ... – PowerPoint PPT presentation

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Title: Cartography: the science of map making

1
Cartography the science of map making
2
Locating yourself on a Globe
• You need a frame of reference
• That is the purpose of Latitude and Longitude
• Defining these parameters
• Earth rotates on an imaginary axis North and
South Poles
• Equator is a great circle that lies equidistant
between them.

3
Great Circles
• ..are imaginary circles of the surface of the
earth who's plane passes through the center of
the earth.
•
• The circumference of the earth is 25,000 miles of
40,000 km
• "Great" because it is the largest possible
circle

4
Great Circles
• 1) cut the earth in half and each half is known
as a hemisphere
• 2) are the circumference of the earth
• 3) provide the shortest routes of travel on the
earth's surface.
• Planes travel in great circles.
• We were always taught a line is the shortest
distance between two points - Not True.
• Small circles circles whose planes do not pass
through the center of the earth.

5
Latitude
• Latitude is the angular distance north or south
of the equator.
• 1 of latitude 112 km 360/40,000 km
• 1 degree 60 minutes
• 1 minute 60 seconds 3649'52" N
• ArcView uses Decimal Degrees
• Sextant measures the angular distance between 2
points (sun horizon)
• So it easy to determine latitude.

6
Longitude
• Longitude no natural reference point
• In 1884 by International Agreement Greenwich
England was the chosen starting point.
• This is called the prime meridian or zero degrees
and everything is east or west of that.
• (angular distance from Greenwich, England)

7
The global grid
• Parallels lines of latitude, only the equator is
a great circle all other parallels are small
circles (they never meet)
• Meridians these are line of longitude and when
joined with its mate half way around the globe
form great circles
• the distance between meridians will vary with
latitude

8
Global Coordinate System
• Longitude and Latitude
• Degrees, minutes, seconds
• 1o latitude 110.5 km (equator)
• 1o longitude 111.3 cos(latitude)
• Meridian
• Parallel
• Great and Small Circles

9
How the Earth is Divided
• Hemispheres Northern, Southern, Eastern,
Western

10
Time Zones
• Solar noon most towns used this, defined as when
a vertical stake cast the shortest shadow.
• By the 19th century transportation and
connected towns and cities, the adopt of a
standard time was necessary.

11
Time Zones (continued)
• 1884 at the International Meridian Conference 24
time zones were established.
• Greenwich Mean Time (GMT) Universal time
Zulu time
• 360/24 15 for each time zone, however for
convenience many time zones follow state and
country lines.
• International Date Line where each new day
begins 180th meridian
• Chronometer
•

12
Time Zones
13

Globes
• The Globe is a nearly perfect representation of
the earth, it shows the shape and spatial
relationships of land and water.
• Problem Can only look at 1/2 at a time.
• However globes can not show detail and are big
and clumsy.

14
Benefits of Maps
• Maps are the geographers most important tool.
• Benefits
• reproduced easily and inexpensive
• different scales
• can put an enormous amount of information on a
map
• roads, buildings, property lines, vegetation,
topography
• distribution of land forms

15
Map Features important in GIS
• Areas
• Lines
• width exaggeration
• Points
• size exaggeration

16
On a globe four properties are true
• 1) parallels of latitude are always parallel
• 2) parallels are evenly spaced
• 3) meridians of longitude converge at the poles
• 4) meridians and parallels cross everywhere at
right angles

17
Map Projection
• A map projection is a mathematical formula for
representing the curved surface of the earth on a
flat map.

18
Think of a light bulb
19
Distortions
• distance
• area
• shape
• direction

20
You must make a choice between
• Equivalence equal area relationship throughout
the map, however you get distorted shapes.
• Conformal shapes are true and meridians and
parallels are at right angles, however land
masses are greatly enlarged at high latitudes.
• Except for very small areas Conformality and
Equivalence are mutually exclusive.
• There are over 1000 different projections.

21
Other types of considerations
• Equidistant projections However scale is not
maintained correctly by any projection throughout
an entire map
• True-direction projections or azimuthal
projections, maintain some of the great circle
arcs. (The shortest distance between 2 points on
a globe is the great circle route.)

22
Map Projection
• Distortions are inherent in maps
• Earth is round, map is flat
• Projection is the term used to describe the
process of mapping a round surface to flat paper
• wide variety of projections possible
• each projection causes different distortions to
information

13
23
Map Projections Types
14
24
Cylindrical Projection example Mercator
• Tangent to the globe at the equator. No
distortions at the equator but it increases
moving North or South. Nice rectangular grid.
• Why are they used in Navigation?
• A straight line drawn anywhere on a Mercator
projection is a true compass heading this is
called a rhumb line.
• However, the distance along this line may vary.

25
Variations on Cylindrical Projection
26
Azimuthal Projection example Many Polar
projections
• Plane is tangent to the globe at some point N or
S of the equator or one point on the equator. No
distortion at the point of tangency but it
increases moving away. All directions from the
center are accurate. It is like a view from
space. Can only see half the world at once.
• All great circles passing through the point of
tangency appear as straight lines.
• Good for knowing the great circle path (I.e.
shortest distances, important to navigators.

27
Variations of Azimuthal Projections
28
Conic exampleLambert Conformal Conic
Projection
• One or more cones tangent to one or more
parallels. Best for mid-latitudes in an E-W
direction (U.S.)
• A straight line is almost a perfect great circle
route (planes use this)
• Can be conformal or equivalent

29
Variations on conic projections
30
Transformations
• The conversion between projections involving
mathematical formulas.
• Good GIS packages can do this.
• Overlaying different projections is not possible.

31
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