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Chapter 2

Geography 1400F/G Chapter Notes - Chapter 2: Great-Circle Distance, Universal Transverse Mercator Coordinate System, Mercator Projection

by

Department
Geography
Course Code
GEOG 1400F/G
Professor
Godwin Arku
Chapter
2

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Geography 1400g Chapter Two: Geographic Research and Maps January 16, 2012
A Research Question: What is the Influence of Place on Human Health?
Human health reflects complex interplay two general characteristics: individuals (age, structure, lifestyles)
and circumstances in which they live both environmental and social
Considerable research on relationship of individual factors (smoking) as well as causal relationships between
different environmental conditions and health
Maps
H.J. de Blij, “if a picture is worth a thousand words, a map can be worth a million- but beware” because can
distort reality, use generalization, symbolization to highlight critical info and suppress lower priority details
Map is two dimensional spatial representation of any part of our world
Map Projections
A map projection is system for displaying curved surface of earth on flat sheet of paper
Cartographer tries to flatten earth, something always wrong, duty to select and preserve those relationships
important for the purpose at hand, and to minimize those distortions that are inevitable but unimportant
Best way to model earth’s surface accurately would be show it on a globe, not as convenient as flat maps
Geographers make two different demands
o Show at a glance generalized relationships and spatial content of entire world (have purpose)
o Show detailed content of portions of earth’s surface-cities, regions, countries- without reference to
areas outside zone of interest
To make world map, must decide how to peel map and flatten: either shows tears or stretching
Projections: Geometrical and Mathematical
Task of geographers to construct on flat surface the network of parallels and meridians (the graticule)
A geometrical (perspective) projection (imagined light source inside), graticule is visually transferred from
globe to geometrical figure, such as plane, cylinder, which can be cut, spread out flat
o Surfaces of cylinders, cones, said to be developable surfaces (can be cut, laid flat without distortion)
o Location of theoretical light source in relation to globe surface cause significant variation in
projection of graticule on developable geometric surface
Orthographic projection results from placement of light source at infinity
Gnomonic projection is type of planer projection and is produced when light source is at centre of earth
When light is placed at antipode- point exactly opposite point of tangency (point of contact between globe
and map) a stereographic projection is produced
Each projection scheme presents different arrangement of globe grid to minimize some distortions inherent
Globe Properties and Map Distortions
All flat maps distort in different ways: area, shape, distance, and direction
Area
Cartographers use equal-area or equivalent projections when important for map to show areas of regions in
correct or constant proportion to earth reality
To compare amount of land in two different parts of world, would be misleading visually to use map that
represented same amount of surface area at two different scales
To achieve equivalence, any scale change the projection portrays in one direction must be change in opposite
A map that shows correct relationships always distorts the shapes of regions
Shape
No projection reproduce correct shapes for large areas, but some accurately portray shapes of small areas

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Geography 1400g Chapter Two: Geographic Research and Maps January 16, 2012
True-shape projections called conformal, and importance of conformality is that regions and features “look
right” and have the correct directional relationships (achieved by ensuring latitude and longitude cross at
right angles and scale is same in all directions at any given location
Except for very small area maps, a map cannot be both equivalent and conformal
Distance
Distance relationships almost always distorted, some maintain true distances in one direction
True distance relationships mean length of straight line between two points on map correctly represent great
circle distance between those points on the earth (an arc of great circle is shortest distance between two
points on the earth’s curved surface; equator is great circle and all meridians of longitude are half)
Equidistant maps true distance in all directions is shown from one or two central points, all other locations
are incorrect and greatly distorted
Direction
On azimuthal projections true directions shown from one central point to all other points (azimuth is angle
formed at beginning point of straight line, in relation to meridian)
Directions from points other than central point to other points are not accurate
Which is best?
- Mercator projection (wall maps) best used as a navigation aid because direction is maintained, amount of
distortion increases as move away from equator (northern and southern masses appear larger)
- Gall-Peters better represents area but distorts shape, scale, distance
- Compromise is Robinson projection, neither equal area nor conformal, however it produces more appealing
visualization (later switched to Winkel-Tripel)
- Winkel-Tripel projection modification, minimizes distortion relative to shapes, distances, perspective
Map Scale
- Vital element of every map, generalizes data
- Scale: relationship between size or length of feature on map and same item on earth’s surface, determines
the amount of that generalization
- Larger the fractional value, larger the scale
The Globe Grid
- Key reference points in grid system are North and South poles and equator and prime meridian
- Latitude measures distance north and south of the equator and parallels run east-west
- Longitude is angular distance of east and west of prime meridian and depicted by north-south lines
Properties of globe grid that mapmakers retain are:
1. All meridians are of equal length; each is one-half the length of the equator
2. All meridians converge at the poles and are true north-south lines
3. All lines of latitude (parallels) are parallel to equator and to each other
4. Parallels decrease in length as one nears the poles
5. Meridians and parallels intersect at right angles
6. The scale on the surface of the globe is the same in every direction
How maps show location
- General-purpose, reference, or location maps make up one major class, purpose to show without analysis or
interpretation a variety of natural or human-made features of an area or world as a whole (highway, street)
- Since latitude and longitude are difficult to use, Military Grid, Civilian Grid System, and Universal Transverse
Mercator (UTM) coordinate system have been developed
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