chapter 7 visualization of geographic information and generation of information products
TRANSCRIPT
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Chapter 7
Visualization of Geographic Information
and
Generation of Information Products
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Principles of cartographic design
1. use of color
2. use of text
3. symbols and symbol sets
4. map-to-page transformation
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Use of color
The primary function of color is to make information on a map visually distinguishable
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Dimensions of color
Hue dominant wavelength (i.e., color)
Value how light or dark a given hue is
Saturation purity of hue (range of reflected wavelengths
see Figure 7.12 on color insert
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• Hue is generally used to indicate qualitative (nominal) differences across the map area
• Value and saturation are typically used to represent quantitative (ordinal, interval, or ratio) differences across the map area
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Note!!!
It is impossible to exactly replicate colors shown on soft-copy and hard-copy since monitor colors are created by additive mixing and printer colors are created by subtractive mixing
see figure 5.30
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Use of text
• Descriptive text is used to give a map its title, to explain the legends and label features.
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Text characteristics:
• Family Arial vs Helvetica• Style (face) bold vs italic
• Font 32 point vs 48 point• Color black vs blue
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ArcInfo
Text stored as either:
(a) symbols of a coverage
(b) annotation coverage
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Symbols and symbol sets
a symbol is a graphic pattern that is used to represent a feature on a map (see Figure 7.14)
• Marker symbol points and nodes (.mrk)• Line symbols arcs (.lin)• Shade symbols polygons (.shd)• Text annotation (.txt)
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Symbol sets
each symbol must be programmed individually, so GIS software packages usually supply the user with predefined symbol sets that can be edited and customized
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Map-to-page transformation
• Physical page actual surface of display medium
• Graphics page portion of physical page where map is drawn
• Map limits portion of graphics page where coverage features are drawn
• Map extent area of the earth’s surface to be displayed (in actual ground units)
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Map-to-page transformation
• Physical page actual surface of display medium
• Graphics page portion of physical page where map is drawn
• Map limits portion of graphics page where coverage features are drawn
• Map extent area of the earth’s surface to be displayed (in actual ground units)
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Map composition
• Map layout design
• Geographical contents
• Label placement
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Map layout design
cartography is both a science and an art, therefore subjectivity and creativity play an important role in the aesthetic quality of a map
see Figure 7.16
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Geographic contents
elements to be included are governed by:
• Map theme i.e., land use
• Map coverage Illinois vs. U.S.
• Map scale level of generalization
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Label placement
• Good label placement ensures readability and enables the reader to associate labels with the map elements that they describe.
• Guideline for automated placement of labels
(see Table 7.3)
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Geographic contents to be considered:
• Visual balance location/proportionality
• Visual clarity generalization
• Visual hierarchy font & symbol size
• Visual contrast use of color and shading
• Context selection of data layers
• Text annotation of features
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Cartographic generalization
Why?
When?
How?
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Why?
• When geographic data are gathered at a scale that is larger than the scale at which they are presented, it is necessary to reduce the complexity of the data to make the resulting map more aesthetically pleasing.
• Generalization ensures that geographic data are presented at a scale appropriate to the purpose of the map and the application requirements of the user.
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How? (see pg. 247)
• Simplification• Smoothing• Aggregation• Amalgamation• Merging• Collapse• Refinement• Typification• Exaggeration• Displacement• Classification
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When?• Congestion
– too many features in too little space
• Coalescence– features touch due to inadequate symbolization
• Conflict– feature symbol incompatible with background
• Complication– data from different sources or at different scales or levels of
tolerance
• Inconsistency– Generalization applied in a nonuniform fashion across map
• Imperceptibility– Feature falls below minimum resolution of map