PROPORTIONAL
SYMBOL
MAPPING
Cartographic Design for GIS (Geog. 340)
Prof. Hugh Howard
American River College
PROPORTIONAL
SYBMOL MAP
DEFINED
PROPORTIONAL DEFINED
•
Proportional Symbol Map
– Map in which point symbols vary in size
according to differences in magnitude of
an attribute (variable)
PROPORTIONAL DEFINED
•
Proportional Symbol Map (cont.)
– The circle is most widely used shape, but
other shapes can be used
PROPORTIONAL DEFINED
•
Proportional Symbol Map (cont.)
– Quantitative in nature
– Point symbols are unlike those on a dot
map, which have the same size and value
Dot Map Legend
Proportional Symbol
Map Legends
PROPORTIONAL DEFINED
•
Confusing terminology…
– Your textbook uses the term “Proportional”
– ArcMap uses “Proportional” or
“Graduated,” depending on the scaling
method used 
•
In ArcMap
– Proportional Symbols
= Mathematical Scaling
– Graduated Symbols
= Range-Graded Scaling
APPROPRIATE DATA
TRUE vs. CONCEPTUAL DATA
•
True Point Data
– Data collected at discrete points
– Weather stations, seismometers, etc.
The point location is known
for each feature or
phenomenon
(x,y or lon,lat)
TRUE vs. CONCEPTUAL DATA
•
Conceptual Point Data
– Data collected for enumeration units
– Symbol is placed in the center of polygon
The center can be the
geometric center (centroid),
or the visual center
TRUE vs. CONCEPTUAL DATA
•
The distinction is sometimes blurry
– Enumeration units represented at small
scales are treated as points
Points are county
centroids, but county
boundaries are not shown
DATA STANDARDIZATION
•
Unstandardized, raw data are more
commonly used
– Standardization can be useful
– Compensate for size of enumeration units
(conceptual point data), etc.
DATA STANDARDIZATION
•
When standardizing conceptual point
data, consider the choropleth instead
– Choropleth maps excel at representing
standardized areal data
MAP PROJECTIONS
and the
PROPORTIONAL
SYMBOL MAP
MAP PROJECTIONS
•
Equivalent (Equal Area) projections are
most appropriate
– Distortion of relative sizes of areas can
mislead the map user
Conformal
Equivalent
SYMBOL SHAPES
SYMBOL SHAPES
•
•
Various symbol shapes can be used
Two categories of point symbol
– Geometric
– Pictographic
Geometric
Do not look like the thing
being mapped
Pictographic
Do look like the thing
being mapped
SYMBOL SHAPES
•
The circle is the most widely used
– Compact and visually stable
– Users prefer over other geometric symbols
– Easy to construct and scale (PI r2)
SYMBOL SHAPES
•
The square is a bit more awkward than
the circle
– Blocky nature isn’t as efficient with space
– Area of a square can be more accurately
estimated (L2)
SYMBOL SHAPES
•
Pictographic symbols
– Can be very effective
– Should be closely related to the theme
– Complex symbols are potentially more
difficult to interpret in congested areas
SYMBOL SHAPES
•
“3D” Symbols
– We aren’t good at estimating volumes
– Employ 3D symbols for aesthetic
purposes, but don’t expect the map user
to estimate volumes
SCALING METHODS
SCALING METHODS
•
There are three primary methods of
scaling, or sizing, proportional symbols
– Mathematical (Directly Proportional)
– Perceptual
– Range Graded
SCALING METHODS
•
Mathematical
– The area of the point symbol is directly
proportional to the data value
350 / 175 = 2
Area of the circle
representing 350 is twice
that of the circle
representing 175
SCALING METHODS
•
Mathematical (cont.)
– Equivalent to an unclassed choropleth
– Legend shows representative values
SCALING METHODS
•
Mathematical (cont.)
– Difficult to interpret, because the map user
can only differentiate a given number of
symbol sizes—10 at most
– Studies indicate that map readers tend to
underestimate the areas of larger symbols
SCALING METHODS
•
Perceptual
– Symbols are systematically enlarged
toward the higher end of the range
SCALING METHODS
•
Perceptual (cont.)
– Compensates for the map user’s tendency
to underestimate areas of larger symbols
Perceptual
scaling is not
widely used
today
SCALING METHODS
•
Range-Graded
– Involves the organization of data values
into classes, or ranges
Values are classified
much like a
choropleth map
SCALING METHODS
•
Range-Graded (cont.)
– Ranges are associated with a limited
number of easily differentiated symbols
SCALING METHODS
•
Range-Graded (cont.)
– Equivalent to a classed choropleth
– Employs a limited number of symbol
sizes, allowing the map user to determine
the general value using the legend
SCALING METHODS
•
Range-Graded (cont.)
– Map-design research has provided
guidelines for selecting symbol sizes that
are easily differentiated
SCALING METHODS
•
•
Range-Graded (cont.)
Possibly the best scaling method
– Readers can easily discriminate symbol
sizes and match them to legend symbols
RangeGraded
Mathematical
Range graded provides greater contrast in circle sizes,
but the result is more generalized
SCALING METHODS
•
•
Range-Graded (cont.)
Especially useful for pictographic
symbols
– It is difficult to estimate areas of complex
shapes
•
•
Classification can be achieved using
any data classification method
Doesn’t work well if the map user fails
to consult the legend
SYMBOL OVERLAP
SYMBOL OVERLAP
•
Trial-and-error is required to produce a
map with suitable symbol overlap
Neither “too full,”
nor “too empty”
SYMBOL OVERLAP
•
Symbols can be differentiated by
applying contrast
No contrast
White outlines
SYMBOL OVERLAP
•
Symbols can be differentiated by
applying contrast (cont.)
Black outlines
Transparency with outlines…
REDUNDANT
SYMBOLOGY
REDUNDANT SYMBOLOGY
•
The use of more than one visual
variable to differentiate point symbols
– To reinforce the idea of increasing
magnitudes
Quantitative Visual Variables
REDUNDANT SYMBOLOGY
•
In addition to varying sizes of symbols,
lightness and hue can be incremented
Lightness
(Monochromatic Sequential)
Hue-Lightness
(Part-Spectral Sequential)
REDUNDANT SYMBOLOGY
•
•
Lighter colors: lower values
Darker colors: higher values
LEGEND DESIGN
LEGEND DESIGN
•
Representative symbols can be
arranged in two fashions
– Linear
– Nested
Linear-Legend
Arrangement
Nested-Legend
Arrangement
LEGEND DESIGN
•
Linear-Legend Arrangement
– Symbols placed adjacent to one another
– Vertical or horizontal orientation
More = Higher
More logical
ordering of
ranges
LEGEND DESIGN
•
Linear-Legend Arrangement (cont.)
– Symbols placed adjacent to one another
– Vertical or horizontal orientation
Values progress like on a
number line
Illogical ordering of ranges
LEGEND DESIGN
•
Nested-Legend Arrangement
– Smaller symbols drawn within larger
– Requires less available space than linear
More logical
ordering of
ranges
More = Higher
Less logical
ordering of
ranges
LEGEND DESIGN
•
Placement of legend definitions
Adjacent to
Symbols
Adjacent with
Leader Lines
Within
Symbols
LEGEND DESIGN
•
•
Which representative symbols should
be included?
Range-Graded Scaling
– One for each class
– Easy visual discrimination
LEGEND DESIGN
•
•
Which representative symbols should
be included? (cont.)
Mathematical or Perceptual Scaling
– Largest, smallest, and intermediate
– Easy visual discrimination
Alternatively, include symbols that are similar in size to the
most common sizes on the mapped area
LEGEND DESIGN
•
Nested-legend used to differentiate
between increase and decrease
LABELING
PROPORTIONAL
SYMBOLS
LABELING SYMBOLS
•
Proportional symbols should be labeled
as ordinary point symbols
– According to the guidelines presented in
the Typography lecture
Sequence of
Preferred Locations
TIPS FOR LABELING
AREAS
LABELING AREAS
•
Default labeling style
LABELING AREAS
•
Convert to upper case
UCase([STATE_NAME])
LABELING AREAS
•
Exaggerate letter/word spacing
LABELING AREAS
•
Screen back (it’s base information)
(Water labels
should be
100% Cyan)
TIP FOR FILTERING
LABELS
FILTERING LABELS
•
Use VBScript in label expression
–
To show only certain labels
Function FindLabel ([CNTRYNAME])
if ([CNTRYNAME] = "France" OR [CNTRYNAME] = "Italy") then
FindLabel = Ucase([CNTRYNAME])
end if
End Function
FILTERING LABELS
•
Use VBScript in label expression
–
To hide certain labels
Function FindLabel ([CNTRYNAME])
if ([CNTRYNAME] <> "France") then
FindLabel = Ucase([CNTRYNAME])
end if
End Function
TIPS FOR FILTERING
FEATURES
FILTERING FEATURES
•
All cities
FILTERING FEATURES
•
Belgian cities
FILTERING FEATURES
•
Large Belgian cities
FILTERING FEATURES
•
Large Belgian and large Dutch cities
PROPORTIONAL
SYMBOL
MAPPING
Cartographic Design for GIS (Geog. 340)
Prof. Hugh Howard
American River College