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