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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

But more abstract so difficult to interpret33

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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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