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Map
A spatial representation of the environment
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Cartographic map
a graphic representation of the environment
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Egocentric
direct experience
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Geocentric
mentally orient yourself with respect to external environment
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Map Characterisitcs
- (Mapness)
- vertical or oblique view of the environment
- drawn to scale
- drawn on a map projection
- generalized and symbolized representation
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what makes maps popular?
- convenient to use
- simplify our surroundings
- are credible documents
- have strong visual impact
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Thematic maps
focus on specific subject and be organized
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Map Use
process of obtaining useful information from one or more maps to help you understand the environment and improve mental map
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How does an image differ from a cartographic map?
- variable scale
- not on a map projection
- generalized?
- symbolized?
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Graticule
- Parallels and Meridians
- use to locate features by their coordinates
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Parallels
- (latitude)
- equally spaced east - west
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Meridians
- North - South lines
- (longitude)
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Numerical range of Latitude
- 0 degrees to 90 degrees
- Spacing = 69.2 mi. per deg.
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Numerical range of Longitude
0 degrees to 180 degrees
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Degrees, Minutes, Secs to Decimal Degrees
Degrees + min/ 60 + seconds/3600
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Spacing of meridians
69.2 mi/ deg. * cosine (latitude)
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Great Circle
largest possible circle that could be drawn on the surface of the spherical earth
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Antipodal meridian
180 degree meridian opposite from prime meridian
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Quadrilaterals
areas on earth bounded by equal increments of latitude and longitude
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Oblate Ellipsoide
parallels are not spaced equally as on a sphere
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Geodetic latitude
- angle made by a line perpendicular to ellipsoid surface at the parallel and equator line
- is on large scale maps
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Geoid
- surface where gravity is the same as at mean sea level (MSL)
- elevation measure by geoid, but GPS uses ellipsoid
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Representative Fraction (RF)
1/x = map distance / ground distance
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Ways of specifying scale
- 1. RF 1:24,000
- 2. Scale statement : one inch to 20,000 ft
- 3. Scale bar
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Calculating RF from a known terrestrial feature:
1 mi wide section of land = 1.01 in on map
- 1/x = 1.01in / (1 mi. * 63,360 in /mi)
- = 1.01 in / 63,360 in
- x = 63,360 in / 1.01 = 62,500
- 1:62,500
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Calculate RF from reference material:
1:62,500 distance between roads 5.69 in and 7.42 in on your map
- 1/62,500 = 5.69 in1/x 7.42 in
- x = 62,500 = 5.69 in /7.42 in = 47,900
- 1:47,900
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Calculating RF from spacing of parallels and meridians:
2 parallels separated by 30 minutes of lat to be 4.37 inches apart on map
- 30 minutes of lat = .5 deg *69.2 mi/deg = 34.6 mi
- 1/x = 4.37 in /34.6 mi
- = 4.37 in / (34.6 mi *63,369 in/mi)
- x = 34.6 mi *63,360 in/mi / 4.37 mi
- 1:502,000
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Map Projection
geometrical transformation of the earths spherical or ellipsoidal
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Geometric Distortions on Maps
- continuity
- correspondence relations
- distance
- area
- direction
- shape
- completeness
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Geoid
project earths irregular surface topography onto a more regular imaginary surface.
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Three map projection families
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Tangent - Case
Projection surface may either touch the globe at a point (point of tangency) or along a line (line of tangency)
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Secant - Case
planar projection surface intersects the globe along a small - circle line of tangency
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Azimuthal Projections
- (planar projections)
- projecting onto a plane tangent to the globe at a point
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Azimuthal
projections that preserve global directions
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Conformal
- angles on the globe are preserved on the map
- "correct form or shape"
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Equidistance
preservation of distance on a map projection
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Aspect
Location of the point or line(s) of tangency on the generating globe
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What are the 4 map projection properties?
- Azimuthal
- Conformal
- Equidistance
- Equal Area
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Four map projections on geometric distortions
- mercator cylindrical conformal
- transverse mercator
- lambert conformal
- alberts equal area
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Orthographic
- projection is how the earth would appear if view from a distant planet
- all rays of light are infinite and parallel
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Stereographic
projecting a light source from the antipodal point on the generating globe to the point of tangency
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Gnomonic
- earliest map projections, first used for star maps by Greek scholar Thales of Miletus in 6th century B.C.
- all great circles on the earth are shown as straight lines
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Azimuthal equidistant
- projection in its polar aspect has the distinctive appearance of a dart board - equally spaced parallels and straight- line meridians radiating outward from the pole
- all straight lines drawn from point of tangency are great circle routes
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Rhumb Lines
all lines of constant compass direction; are straight lines on mercator map
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Peters Projection world map
showed 3rd world countries more fairly
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Transverse Mercator
Rhumb lines are not straight lines; north - south of earth are projected with no local shape distortion and little distortion in area
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Universal Transverse Mercator (UTM)
84 degrees N to 0 degrees to 80 degrees S latitude
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Cartesian Coordinates
square grid on the map with divisions left to right on horizontal X axis and divisions bottom to top labeled on a vertical Y axis
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State Plane Coordinates
created in 1930's by land surveying in US define property boundries
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Metes and Bounds System
- Property Boundry
- Legal property description tied to earth features and remained useful as long as neighbors agreed with place names and accepted the boundries
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French Long Lots
- Along rivers or lakes = chief source of transportation and communication for French
- waterfront as parallels lines, creating narrow ribbon farms or long lots
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US Public Land Survey (USPLSS)
- Township and Range System
- Prior to settlement and required all grants be recorded
- 1-36
- 37< = Donation Land Claims
- Prinicpal Meridians and Base Lines
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External Errors
- impose methods on the map from the outside
- judgements, calcualtions, methods
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Internal Errors
distortions in a map
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Physical measurement for distance
- use scale bar
- use latitude as a scale bar
- use map rulers
- use mechanical measuring devices
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Orienting by Inspection
- 1 liner feature
- 2 liner features
- Prominent objects
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Magnetic Declination
angular difference between true and magnetic
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Agonic Line
true and magnetic north poles are aligned
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Compass Points
early mariners, use winds to find their way
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Wide Area Augmentation System (WAAS)
GPS correction data for precision aircraft positioning
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GPS
Global Positioning System
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