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Geography 38:286 Computer Cartography

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Symbolization. Simplification. Inevitable loss and/or reduction in data quality. Selection ... Symbolization. Symbols represent real world objects. Two types of ... – PowerPoint PPT presentation

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Title: Geography 38:286 Computer Cartography


1
Geography 38286 Computer Cartography
  • Topic 1 Introduction to Thematic Mapping
  • Chapter 1 Dent, et al.

2
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

3
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

4
The Need For Maps
  • Record, display, store, and analyze spatial
    information
  • Reveal spatial patterns and relationships not
    otherwise visible

MAPPING
5
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

6
Cartography is
  • The art, science, and technology of creating maps
  • Includes study of the theoretical foundations of
    mapping
  • graphic communication
  • colour theory
  • map interpretation

7
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

8
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

9
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

10
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

11
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

12
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

13
  • Map Types
  • Mental
  • Tangible (Real)
  • Virtual
  • Reference
  • Thematic
  • Quantitative
  • Qualitative
  • Multi-Variable
  • Single Variable

Figure 1.3, Dent
14
Map Scale
  • Scale indicates amount of reduction
  • Essential info if map is used to determine
  • Distances
  • Areas
  • Slope

15
Large vs. Small Scale Maps
1250,000 Small Scale
16
Large vs. Small Scale Maps
125,000 Large Scale
17
Expressions of Scale
  • Ratio or Fraction
  • 150,000 1/250,000
  • Advantage unitless

Map
Map
Real World
Real World
18
Expressions of Scale
  • Verbal or Written
  • 1 cm 50 km
  • 1 in 1 mile
  • Advantage easily understood

19
Expressions of Scale
  • Linear or Bar Scale
  • Advantage survives reduction/enlargement

20
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

21
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

22
Scale Conversions
  • Linear or Bar Scale to Written
  • 1 cm 500 km

23
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

24
Large Area/Extent
1250,000 Small Scale
25
Small Area/Extent
125,000 Large Scale
26
Small Map Size (given study area)
1250,000 Small Scale
27
Large Map Size (given study area)
125,000 Large Scale
28
Less Detail
1250,000 Small Scale
29
More Detail
125,000 Large Scale
30
More Abstraction
1250,000 Small Scale
31
Less Abstraction
125,000 Large Scale
32
Effects of Scale
Map Scale
Large
Small
Less
More
Level of Abstraction
After Figure 1.14, Dent et al.
33
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

34
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

35
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

36
Classification
  • Organization of data into groups/categories
  • Reduces complexity
  • Selection of class boundaries v. important (more
    on classification later)
  • Loss of information

37
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

38
Simplification
  • Generalization of actual map features
  • Simplifying complex lines, borders, boundaries
  • Amount dependent on scale
  • Determines level of detail

39
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?

40
Next Topic Geodesy Chapter 2, Dent, et al.
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