MAPPING EXERCISE Thematic Mapping: The Flow Map The flow ...
Topic 10: Other Thematic Mapping Techniques · 2017-11-27 1 Geography 38/42:286 GIS 1 Topic 10:...
Transcript of Topic 10: Other Thematic Mapping Techniques · 2017-11-27 1 Geography 38/42:286 GIS 1 Topic 10:...
2017-11-27
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Geography 38/42:286
GIS 1
Topic 10:
Other Thematic Mapping Techniques
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What is an Isarithmic Map?
Portrays continuous surfaces using isolines
Represent constant value
Located with reference to control points
Surface may be:
real (e.g. a topographic, or barometric surface)
or conceptual (e.g. population or tortoise density)
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When Is It Used?
Feature to be mapped is continuous in nature
Or can be visualized as a surface
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Spatial Data Characteristics
Two types of isarithmic maps
Different spatial data characteristics
Isometric
Isoplethic
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Asaptial Data Characteristics
For Isometric form:
Raw or derived values may be used:
For Isoplethic form:
Derived values used; never raw values
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Other Considerations
Legend design
Ancillary information, base map info
Line symbols and labels
Map projection
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What is Flow Mapping?
Depicts movement of phenomena
Uses line symbols of varying type/width
May indicate direction with arrows
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When Is It Used?
Only option when objective is to show:
movement/flow
spatial interaction/connectivity
Can show more than one phenomena
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Types of Flow Maps
Qualitative
Flow of different types of objects
Quantitative
Flow of different quantities of objects
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Flow Line Placement
Line symbols may:
Show actual path
Stylized path
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Actual Flow Paths
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Stylized Flow Paths
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Spatial Data Characteristics
Can be used to map flow:
Between discrete point locations
Between discrete areal units
Along discrete line features
for attributes (things) that flow/move
Not continuously distributed phenomena
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Aspatial Data Characteristics
Depict raw data values only
Derived data do not flow
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Types of Flow Maps
Variations based on direction and pattern of flow
Radial Multiple sources to/from a central location; 1-way flow
Distributive Multiple sources to multiple destinations; 1-way flow
Network Interconnectivity b/w multiple locations; 2-way flow
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Types of Flow Maps
Radial
Network
Distributive
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Other Considerations
Legend design
Ancillary information, base map info
Map projection
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What is a Value by Area Map?
Portrays areal units such that area is scaled
proportionately to value/magnitude of interest
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What is a Value by Area Map?
Size is in no way related to actual
geographic area/extent
No other symbolization used
Shape and relative position of areal units
preserved as much as possible
Also called cartograms
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When Is It Used?
Used when map reader is familiar with
study area (size/shape of areal units)
High shock value when mapped area is
significantly different than true area
Otherwise, better options
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Types of Value by Area Maps
Two types based on contiguity of areal units
Contiguous Cartograms
Adjacency of areal units maintained
Requires considerable generalization and/or
distortion of internal boundaries
Easier for map reader to identify area
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Contiguous Cartogram
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Types of Value by Area Maps
Noncontiguous Cartograms
Adjacency not maintained
Areal units placed in correct relative position &
orientation but with gaps between
Easier to construct
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Noncontiguous Cartogram
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Spatial Data Characteristics
Data represents discrete areal units
At least three other options
Not possible to represent continuous
data or discrete point or lines
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Aspatial Data Characteristics
Can be used to depict raw or derived
data Better when there is significant variability in size
Best when values are opposite to true area
e.g. so small areas are big and big areas are little
No or few zero data values allowed
Exceptions must be noted
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Other Considerations
Legend design
Ancillary information
Base map info
Map projection
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