Domain analysis by means of the visualization of maps of ...
Maps Basic models and means of communication used by ...
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Maps
Chapter 2
Maps
⚫ Basic models and means of communication
used by geographers to depict the earth’s
surface.
⚫ Map – a representation, normally to scale and on a
flat medium, of a selection of material or abstract
features on, or in relation to, the surface of the
earth.
⚫ Map not drawn to scale?
Maps as the Tools of
Geography
• Maps are the primary tools of spatial analysis
• Cartography - The art, science and technology of
making maps
• All maps have some error (distortion) inherent
•3D space represented in 2D
The Geographic Grid
⚫ Set of imaginary lines that intersect at right angles to form a system of reference for locating points on the surface of the earth
⚫ Position on the Earth is determined by the grid system of latitude
and longitude and are measured in:
⚫ degrees, minutes and seconds -
⚫ 45° 27’ 15”
⚫ decimal degrees
⚫ 45.4542
⚫ Key reference points⚫ North and South Poles, (90° N & S)
⚫ Equator (0 °)
⚫ prime meridian (0°)
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The Geographic Grid
⚫ Latitude
⚫ Angular distance north or south of the equator
⚫ Measurements ranging from 0°(equator) to 90° (poles)
⚫ Lines (parallels) are parallel and run east-west
⚫ Distance between each degree ≈ 69 miles
⚫ Can be subdivided into minutes and seconds
The Geographic Grid
⚫ Prime meridian (0°)
⚫ Starting point for east-west
⚫ Passes through Greenwich, England
⚫ Longitude
⚫ Angular distance east or west of the
prime meridian
⚫ Measurements ranging from 0° (prime
meridian) to 180°
⚫ Lines (meridians) are farthest apart at
the equator and converge at the poles
The Geographic Grid
⚫ Time depends on longitude
⚫ Greenwich mean time (GMT)
⚫ Time at the prime meridian
⚫ International Date Line
⚫ Where each new day begins
⚫ Generally follows the 180th meridian
Map Projections
⚫ Earth can be represented with reasonable accuracy only on a globe
⚫ Globe properties⚫ All meridians are equal in length
⚫ All meridians converge at the poles
⚫ Lines of latitude are parallel to the equator and to each other
⚫ Parallels decrease in length as one nears the poles
⚫ Meridians and parallels intersect at right angles
⚫ The scale on the surface of the globe is the same everywhere in all directions
Map Projections
⚫ A map projection is the mathematical transformation of space from the surface of the earth to that of a flat plane.⚫ curved surface of the earth, on a flat medium
⚫ some distortion is inevitable
⚫ Distortion - least for small areas and greatest when a map attempts to show the entire surface of the Earth.
⚫ All flat maps distort some or all of the four main
properties of actual earth surface relationships:
⚫ Area
⚫ Shape
⚫ Distance
⚫ Direction
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Map Projections
⚫ Greenland vs. South America
⚫ Which one is bigger?
Map Projections
⚫ Equal-area (equivalent) projections
⚫ Areas are in correct proportion to earth reality
⚫ Shape is distorted
Map Projections
⚫ Conformal projections - Shape
⚫ Shapes of small areas are accurately portrayed
⚫ No projection can provide correct shapes for large areas
⚫ Area is distorted
Map Projections
⚫ Equidistant projections - Distance
⚫ Distances are true in all directions from one or two
central points
⚫ Distances between all other locations are incorrect
⚫ A map cannot be both equidistant and equal-area
⚫ Robinson projection
⚫ Compromise between equal-area and conformal
⚫ Fairly realistic view of the world
⚫ Distortion is greatest in less populated places
(N. Canada
Greenland
⚫ Russia)
⚫ US 3%
smaller
⚫ Canada
21% larger
Map Projections Scale
⚫ Ratio between the measurement of something
on a map and the corre-
sponding measurement
on the earth
⚫ Represented in three ways
⚫ Verbal
⚫ Graphic
⚫ Representative fraction
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Scale
⚫ Can range from very large to very small
⚫ Large-scale maps
⚫ A large scale map covers a small area and shows
great detail.
⚫ Ratio of map to ground distance is relatively large
⚫ RF is large, e.g. 1/10,000
⚫ Small-scale maps
⚫ A small scale map covers a large area and shows
only large or prominent features.
⚫ Ratio of map to ground distance is smaller
⚫ RF is small, e.g. 1/100,000,000.
Effects of Scale
⚫ Scale controls not only how features are shown, but what features are shown. ⚫ Scale also controls the level of detail and hence the purpose of
the map.
Types of Maps
Topographic Maps and Terrain
Representation
⚫ Topographic maps are general-purpose maps
⚫ Depict the shape and elevation of terrain
⚫ Natural and human features
⚫ USGS topographic map series
⚫ Depicting relief (variation in elevation)
⚫ Spot heights
⚫ Contour lines
⚫ All points along line are of equal elevation above a datum
plane, usually mean sea level
⚫ Contour interval is the vertical spacing between contour lines
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Thematic Maps and Data
Representation
⚫ Thematic Maps: a map that
shows a specific spatial
distribution or category of
data
⚫ Qualitative maps
⚫ Show the distribution of a
particular class of information
⚫ Locations of oil fields, national
parks or crop specialization
Thematic Maps and Data
Representation
⚫ Quantitative maps
⚫ Show the spatial characteristics of numerical data
Thematic Maps and Data
Representation
⚫ Point symbols
⚫ Dot maps
⚫ Each dot represents a
given quantity
⚫ Graduated symbol
maps
⚫ Size of symbol varies
according to quantities
represented
Thematic Maps and Data
Representation
⚫ Area cartograms ⚫ Areas of units are drawn proportional to the data they
represent
⚫ Left: Traditional view of the election
⚫ Right: Size proportional to population – instead of land area
States are sized
Relative to the
Number of residents.
Thematic Maps and Data
Representation
⚫ Line symbols
⚫ Various symbols represent features that have length
but insignificant width
⚫ Examples?
⚫ Isoline maps
⚫ Lines of constant value
⚫ Flow-line maps
⚫ Portray linear movement between places
Map Misuse
⚫ Message conveyed by a map reflects the intent and, perhaps, biases of its author
⚫ Techniques for making misleading maps⚫ Lack of a scale
⚫ Simple design that omits data or features
⚫ Colors with a strong psychological impact
⚫ Bold, oversized, and/or misleading symbols
⚫ Action symbols
⚫ Selective omission of data
⚫ Disinformation
⚫ Inappropriate projection
⚫ During Cold War – Russia admittedly falsified information on their public maps.
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Remote Sensing
⚫ Obtaining images of an area from a distance
⚫ Aerial photography⚫ Standard photographic film
⚫ Infrared film⚫ False-color images
⚫ Nonphotographic imagery⚫ Thermal scanners
⚫ Radar
⚫ Lidar (light detection and radar
⚫ Satellites⚫ Landsat satellites
Geographic Information
Systems (GIS)
⚫ Computer-based set of
procedures for gathering, storing,
manipulating, analyzing, and
displaying geographically
referenced data
⚫ Geographic database
⚫ Digital record of geographic
information
⚫ Maps, surveys, aerial photos, satellite
images, etc.
⚫ Purpose of study determines data
World Health Threats
⚫ Cholera
⚫ Dr. John Snow –
created first crude GIS
⚫ Overlaid map of cholera
victims over map of
water pumps and
streets.
Applications of GIS
⚫ Various fields for a variety of purposes, including:
⚫ Biologists and ecologists: studying environmental
problems
⚫ Epidemiologists: studying diffusion of diseases and
entomological risk factors
⚫ Political scientists: evaluating legislative districts
⚫ Sociologists: examining patterns of segregation
⚫ Private sector companies: site selection, analyzing
sales territories, calculating optimal driving routes
⚫ Government: transportation planning, analyzing
patterns of crime, responding to disasters
Virtual and Interactive Maps
⚫ Maps are widely available on the internet
⚫ Google Earth
⚫ Combines aerial photos, satellite images, and maps
with street, terrain, and other data
⚫ Mashups
⚫ Digital maps merged with data from other sources
⚫ Interactive mapping