GEOG assignment
jp23jpl
1
Scale & Projection
Two Key Ideas
Scale
Map distance < ground distance
Projection
Going from round earth to flat map
Scale
Map scale: relationship between map units and real units
Ratio scale: representative fraction (RF) = map:ground distance
Graphic scale (e.g., bar scale )
Verbal scale (e.g., ‘One inch represents 800 feet’)
A 3 cm street on a map with an RF of 1:100,000 is how long in reality?
What is a key advantage of a bar scale?
3 cm × 100,000 = 300,000 cm = 3,000 m = 3 km
2
Scale Matters
Scale selection
Map scale
Mapped earth area
Information detail
Large
Large Small
Small
More Less
Scale and Resolution
Data have different resolutions for different uses…
Census data are collected at the household
Reported (tabulated/calculated) at tracts or lower
Mapped at many resolutions
Projection
Globes are realistic = Good
Globes are hard to use = Bad
Not easy to carry
Not easy to work on
Small scale
3
Projection
Projection makes the globe flat
Projection Concepts
Coordinate systems
Projection mechanics
Projection surfaces
Projection properties
Coordinate Systems: The Graticule
Coordinates on 3d globe = the graticule
Longitude ( -180°to +180°)
Prime (Greenwich) Meridian (0°)
International Date Line (180°)
Latitude ( -90° to +90°)
Equator ( 0°)
North Pole ( +90°)
South Pole ( -90°)
4
One degree of longitude
at equator (0° latitude)
One degree of longitude
at 60° latitude
Parallels are equally spaced
Meridians converge at poles
Parallels and meridians cross at right angles
Coordinate Systems: Planar
Coordinates on a
2d surface = planar
coordinates
Many kinds of
planar coordinate
systems…
+180°
+85°
-85°
-180° 0°
0°
Mercator Projection
Minneapolis
+44.88°, -93.22°
+20037508 m
+20037508 m
-20037508 m
-20037508 m 0 m
0 m
A single projection can be used with many coordinate systems
Mercator Projection
5
State Plane Coordinate System (SPCS)
Military Grid Reference System (MGRS)
15SWC8081751205
Precision (m):
100000
10000
1000
100
10
1
What3Words
3m x 3m squares
57 trillion squares
cover globe
Three words identify a
square
Easier to remember
than long number
sequences
6
Projection Mechanics
Projection Mechanics
(Dent 1999)
Mechanics: Perspective Approach
Developable Surface
7
Mechanics: Algorithmic Approach
Mollweide Mercator
Developable Surface Types
Plane Cone Cylinder
Tangent Point or Line
Tangent to Sphere at Line Tangent to Sphere at Point
Distortion varies with surface type and intersection of surface with globe
8
Standard Line or
Standard Parallel
Standard Lines or
Standard Parallels
Distortion is minimal at the standard line
Standard Line or
Standard Parallel
Standard Point
(Dent 1999)
Distortion varies with surface type and tangency
9
Projection Properties
Property Map Called Use Interesting Fact
Shape / Angle
Conformal
Orthomorphic
Navigation
Topographic
Meridians and parallels
intersect at right angles
Area Equal-area
Equivalent
Thematic Can be true for whole map
Distance Equidistant Atlas Distance is true along lines of
‘true scale’
Property Map Called Use Interesting Fact
Shape / Angle Conformal
Orthomorphic
Navigation
Topographic
Meridians and parallels
intersect at right angles
Mercator Projection
Property Map Called Use Interesting Fact
Area Equal-area
Equivalent
Thematic
Can be true for whole map
Gall-Peters Projection
10
Property Map Called Use Interesting Fact
Distance Equidistant Atlas Distance is true along lines of
‘true scale’
Azimuthal Equidistant Projection
11
Mercator Projection
Cylindrical & Conformal
Gall-Peters Projection
Cylindrical & Equal Area
Some projections are very different
Lambert Conformal Conic vs. Albers Equal Area Conic
Some projections are quite close
Composite projections combine different projections
Goode’s Homolosine joins Sinusoidal and Mollweide projections
along north and south parallels 40°44’11.8"
Goode homolosine composite projection
Sinusoidal represented between
north and south parallels 40°44’11.8"
Mollweide represented outside of
north and south parallels 40°44’11.8"
12
Interrupted projections cut the surfaces into lobes
Interrupted Goode homolosine
composite projection
Conclusion
Map elements: scale, projection, symbolization
Scale
Scale measures
Scale matters
Projections
Projection mechanics
Coordinate systems
Projection surfaces
Projection properties