Geography 38:286 Computer Cartography

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Geography 38286Computer Cartography

• Topic 1 Introduction to Thematic Mapping
• Chapter 1 Dent, et al.

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Basic Forms of Communication

• Articulacy - spoken
• Literacy - written
• Numeracy - numbers
• Graphicacy - pictures
• If a picture is worth a thousand words
• a map is worth ? ? millions

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What is a Map?

• Map is a (graphic) model
• abstract representation of the real world
• May be real, virtual, or mental
• Basic information is
• Location of features
• Attribute(s) of features at that location

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The Need For Maps

• Record, display, store, and analyze spatial
  information
• Reveal spatial patterns and relationships not
  otherwise visible

MAPPING
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Map Making (Mapping) is

• The selection and collection of data
• Generalizing/organizing data
• Designing and constructing the map
• Transformation of aspatial data to spatial
  information

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Cartography is

• The art, science, and technology of creating maps
• Includes study of the theoretical foundations of
  mapping
• graphic communication
• colour theory
• map interpretation

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The Cartographic (?) Revolution

• Does it exist?
• Result of
• pervasive use of technology
• availability of spatial data
• computer mapping and GIS applications
• increased demand for cartographic products
• More accurately a geospatial information age

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The Cartographic Revolution

• Implications
• increased emphasis on cartographic education
• expertise of cartographers encoded in software
• lack of standards or certification
• who controls/influences development of field?
• renewed interest in geography

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Basic Characteristics of Maps

• All maps
• portray locations and attributes
• are reductions (reduced scale)
• employ transformations or map projections
• use one or more coordinate systems
• are abstractions of reality
• follow conventions

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Kinds of Maps

• 1) General Purpose Maps
• also referred to as reference maps
• portray a variety of information
• no intended use or particular theme
• ex. road maps, topographic map

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Kinds of Maps

• 2) Thematic Maps
• portray a single or associated group of features
• depict a specific theme
• consist of
• base map for locational reference
• one or more thematic layers

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Two Types of Thematic Maps

• 1) Qualitative
• portray nominal or categorical type data
• 2) Quantitative
• portray ordinal, interval, or ratio type data
• single or multiple variables

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• Map Types

• Mental

• Tangible (Real)

• Virtual

• Reference

• Thematic

• Quantitative

• Qualitative

• Multi-Variable

• Single Variable

Figure 1.3, Dent
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Map Scale

• Scale indicates amount of reduction
• Essential info if map is used to determine
• Distances
• Areas
• Slope

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Large vs. Small Scale Maps
1250,000 Small Scale
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Large vs. Small Scale Maps
125,000 Large Scale
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Expressions of Scale

• Ratio or Fraction
• 150,000 1/250,000
• Advantage unitless

Map
Map
Real World
Real World
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Expressions of Scale

• Verbal or Written
• 1 cm 50 km
• 1 in 1 mile
• Advantage easily understood

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Expressions of Scale

• Linear or Bar Scale
• Advantage survives reduction/enlargement

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Scale Conversions

• Ratio or Fraction to Verbal or Written
• 150,000 1/250,000
• 1 cm 50,000 cm 1 cm 250,000 cm
• 1 cm 500 m 1 cm 2,500 m
• 1 cm 2.5 km
• Convert real world side to largest unit
  of measure not resulting in a fraction

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Scale Conversions

• Verbal or Written to Ratio
• 1 cm 50 km
• 1 cm 50 km x 1000m/km x 100cm/m
• 1 cm 5,000,000 cm
• 15,000,000
• 1 in 1 mile
• 1 in 1 mile x 1 mile/63,360 in
• 1 in 63,360 in
• 163,360

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Scale Conversions

• Linear or Bar Scale to Written
• 1 cm 500 km

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Effects of Scale

• The scale of a map determines the
• Geographic area/extent covered
• Size of the final map
• Level of detail shown
• Level of abstraction

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Large Area/Extent
1250,000 Small Scale
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Small Area/Extent
125,000 Large Scale
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Small Map Size (given study area)
1250,000 Small Scale
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Large Map Size (given study area)
125,000 Large Scale
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Less Detail
1250,000 Small Scale
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More Detail
125,000 Large Scale
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More Abstraction
1250,000 Small Scale
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Less Abstraction
125,000 Large Scale
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Effects of Scale
Map Scale
Large
Small
Less
More
Level of Abstraction
After Figure 1.14, Dent et al.
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Selecting an Appropriate Scale

• Map scale is determined by
• INTENDED USE AND AUDIENCE
• Which usually dictates one (or more) of
• Geographic area/extent covered
• Level of detail shown
• Level of abstraction
• Size of the final map
• . . . and establishes the required scale
• Compromise is often required

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Cartographic Abstraction

• Process of transforming unmapped data into
  suitable map form
• Achieved through four processes of
  generalization
• Selection
• Classification
• Symbolization
• Simplification
• Inevitable loss of data and/or reduction in
  quality

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Selection

• First step in generalization process
• Choose data to include/exclude
• Theme Hydrology
• What features?
• Lake
• Rivers
• Wetlands
• What attributes?
• Depth
• Suspended sediment
• Water Quality

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Classification

• Organization of data into groups/categories
• Reduces complexity
• Selection of class boundaries v. important (more
  on classification later)
• Loss of information

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Symbolization

• Symbols represent real world objects
• Two types of map symbols
• 1) Replicative
• Resemble real world equivalent
• 2) Abstract
• Do not resemble real world equivalent
• Choice dependent on scale
• Determines level of abstraction

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Simplification

• Generalization of actual map features
• Simplifying complex lines, borders, boundaries
• Amount dependent on scale
• Determines level of detail

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Graphic (Map) Communication

• Two transformations of map data
• 1) One when the map is created
• We control
• 2) One when the map is interpreted
• No control
• Is the map reader getting the (intended) message?

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