Contents of Lecture
Lecture 3:
Georeferencing System
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Map & Cartography
Elements of Map
Map Projection
Coordinate System
Geography 373
Spring, 2006
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Map
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Cartography
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The graphic representation of spatial
relationships and spatial forms of reality
Maps are reduction/abstraction of reality
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Interface to GIS (view, query, and analyze)
Well-designed map vs. poorly -designed map
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Common Elements of Map
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Map title
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Map body
Map projection
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The making and study of maps in all their
aspects
A process of assembling map elements
design of symbol and text (symbol relationship,
color, classification …)
Techniques concerned with reducing the spatial
characteristics of an area, putting in map form
to make it observable
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Map Projection
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3-D Sphere (Earth) à 2-D Plane (Map)
Map scale
Map Legend
North Arrow
Neat line/ map border
Other information (source, data quality, inset…)
Generalization and symbolization is involved.
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Map Projection
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Map Projection
The process of transforming the spatial
relationship of features on the Earth’s
surface to a flat map
Mathematical equations to convert the
curved surface of the earth to flat map:
flatten the curve!
Every projection has distortion!
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Cylindrical projection
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Projected onto a cylinder
Azimuthal projection
Projected onto a plane (tangent to the globe)
Conical projection
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Projected onto a cone
N o perfect projection! : Area, shape, direction,
or distance distortion.
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Cylindrical Projection
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Near the equator represent well
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Only part of the Earth is visible: half
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Near the pole very distorted
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Direction is preserved
Near the edge very distorted
Universal Transverse Mercator (UTM)
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Conic Projection
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Map Units
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Distance is distorted towards the bottom of
the image
Scale is preserved for most part
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Map units are the units of the view ’s display
surface
map units are the units of base data
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Azimuthal Projection
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If the view has not been projectedà spatial data is
in Decimal Degrees
map units are the units into which the data is being
projected in the view
E.g. state plane = feet, UTM = meter…
Reference to metadata documenting what
units the data is in
C.f.) distance units : the units used by ArcView
to display or indicate. choose the units you
wish to use.
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Map Scale
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Map Generalization
The ratio of distance on a map to
corresponding distance to the Earth
Scale representation
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All maps are generalized
Selected and simplified representation of detail
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1:10,000, 1/10,000
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Verbal Statement: map distance with respect to
earth distance
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Representative Fraction (RF): simple fraction or ratio
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1 inch to 1 mile
Bar Graphic: graphic scale
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Map Generalization
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Cartographic symbol of letter, character,
graphics representing some feature
quality or characteristic on a map
Classes
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Map Symbolization: Objects
point: positional data
Line: linear data
Area: area data
How about volumetric data such as
population of city?
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Map Symbolization
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Depends on scale, objective (purpose), graphic
limits, quality of data
By simplification, classification, symbolization,
induction
Surface
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Map Symbolization: Data Types
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Coordinate Systems
Geographic Coordinate Systems
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Geographic Coordinates
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Rectangular (Cartesian, Euclidean, Plane)
Coordinates
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Latitude & Longitude
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Grid system
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X (easting), Y (northing) coordinates
Distance, direction on the earth
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UPS & SPC
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Centered on the pole
Used for polar regions that extend beyond regions
covered by UTM
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SPC: State Plane Coordinate
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Used unique set of coordinates for each state
• Each zone has its own projection
e.g. long state uses Transverse Mercator, wide state uses
Lambert conformal conic projection.
• More accurate than UTM
• Issue: problematic when study area includes more than
one state
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Most commonly used plane grid system
Divide earth from 84 N to 80 S into 60
vertical zones that are 6 degree of
longitude wide
Each of the 60 zones is divided into the
northern and southern hemispheres.
Separate Mercator projection is applied to
each zone to reduce distortion
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Datum
UPS: Universal polar stereographic
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UTM (Universal Transverse
Mercator)
Rectangular Coordinate Systems
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The basis for calculating the geographic
coordinates of a location. A spheroid is a
required input to the derivation of a datum
A part of the definition of a projected coordinate
system
Many attempts have been made to measure the
earth’s size and shape
- Adopted by U.S. in 1927 (NAD27): North American Datum
- Adopted by U.S. in 1980 (NAD80)
- Adopted internationally in 1980 (GRS80): Geodetic
Reference System
- Refined internationally in 1984 (WGS84): World Geodetic
System of 1984
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Earth X, Y, Z Reference
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Geoid
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Map Projection
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a representation of the surface of the earth that it would assume if the
sea covered the earth, also known as surface of equal gravitational
attraction and mean sea level
sea level isn't level
the vertical coordinate, Z (elevation), is referenced to the geoid
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a smooth elliptical model of the earth's surface
X,Y (horizontal coordinates) are referenced to an ellipsoid
GRS80 is currently the most commonly used elliptical model used for
the globe, though a new ellipsoid has recently been developed by the
National Geodetic Survey and will likely replace GRS80 for future
projects
The Clarke 1866 ellipsoid is a predecessor to the GRS80 ellipsoid
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Units: meters, feet
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Datum: NAD83, GRS80, WGS84, etc
Spheroid: NAD83, GRS80, WGS84, etc
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Zone: 15N, 11S
Geographic coordinates is always base
UTM to Geographic coordinate
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Lambert to Geographic coordinate
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UTM to Lambert
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Lambert to UTM
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Important Terms
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Meters, feet, etc to DD (DMS)
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DD (DMS) to meters, feet, etc
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Projection system
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- Projection system to geographic coordinates
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Datum: NAD83, GRS80, WGS84, etc
Units: DD, DMS
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Between Map Projections
Geographic coordinates
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- Geographic coordinates to projection system
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Map Projection Parameters
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Ellipsoid
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A systematic arrangement of parallels and
meridians on a plane surface.
UTM à Geographic Coordinates
Lambert à Geographic Coordinates
UTM à Geographic Coordinates à Lambert
Lambert à Geographic Coordinates à U T M
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Homework
Map Projection
Map scale
Generalization
Symbolization
Etc.
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Read Chapter 10
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