PROPORTIONAL SYMBOLMAPPING
Cartographic Design for GIS (Geog. 340)Prof. Hugh HowardAmerican 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
Proportional Symbol Map Legends
Dot Map Legend
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 PROJECTIONSand the
PROPORTIONAL SYMBOL MAP
MAP PROJECTIONS• Equivalent (Equal Area) projections are
most appropriate – Distortion of relative sizes of areas can
mislead the map user
EquivalentConformal
SYMBOL SHAPES
SYMBOL SHAPES• Various symbol shapes can be used
• Two categories of point symbol– Geometric– Pictographic
GeometricDo not look like the thing
being mapped
PictographicDo 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
Range graded provides greater contrast in circle sizes, but the result is more generalized
Range-Graded
Mathe-matical
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 = HigherMore logical ordering of
ranges
LEGEND DESIGN• Linear-Legend Arrangement (cont.)
– Symbols placed adjacent to one another– Vertical or horizontal orientation
Illogical ordering of ranges
Values progress like on a number line
LEGEND DESIGN• Nested-Legend Arrangement
– Smaller symbols drawn within larger– Requires less available space than linear
More = Higher Less logical ordering of
ranges
More logical ordering of
ranges
LEGEND DESIGN• Placement of legend definitions
Within Symbols
Adjacent with Leader Lines
Adjacent to 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 ofPreferred Locations
TIPS FOR LABELING AREAS
• Default labeling style
LABELING AREAS
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
• Use VBScript in label expression– To show only certain labels
FILTERING LABELS
Function FindLabel ([CNTRYNAME]) if ([CNTRYNAME] = "France" OR [CNTRYNAME] = "Italy") then FindLabel = Ucase([CNTRYNAME]) end ifEnd Function
• Use VBScript in label expression– To hide certain labels
FILTERING LABELS
Function FindLabel ([CNTRYNAME]) if ([CNTRYNAME] <> "France") then FindLabel = Ucase([CNTRYNAME]) end ifEnd Function
TIPS FOR FILTERING FEATURES
• All cities
FILTERING FEATURES
• Belgian cities
FILTERING FEATURES
• Large Belgian cities
FILTERING FEATURES
• Large Belgian and large Dutch cities
FILTERING FEATURES
PROPORTIONAL SYMBOLMAPPING
Cartographic Design for GIS (Geog. 340)Prof. Hugh HowardAmerican River College