Symbology

Cartographic symbolization

Cartographic symbolization is based on“a systematic approach for selectingthe graphic symbols to use on a map”

Symbolization is the process of creating graphic symbols to represent feature attributes values

The four components of symbolization

featuredimensionality

levelof

measurement

graphicmark

visualvariables

mappingmethod

symbolization

=+ + +

The four components of symbolization

FEATUREREPRESENTATION

ATTRIBUTEREPRESENTATION

`

featuredimensionality

levelof

measurement

graphicmark

visualvariables

mappingmethod

symbolization

=+ + +

FEATURE ATTRIBUTEFEATURE

REPRESENTATIONATTRIBUTE

REPRESENTATION

`

featuredimensionality

levelof

measurement

graphicmark

visualvariables

mappingmethod

symbolization

=+ + +

The four components of symbolization

featuredimensionality

levelof

measurement

graphicmark

visualvariables

mappingmethodsymbolization

=+ + +

FEATURE ATTRIBUTEFEATURE

REPRESENTATIONATTRIBUTE

REPRESENTATION

`

The four components of symbolization

The four components of symbolization

featuredimensionality

levelof

measurement

graphicmark

visualvariables

mappingmethod

symbolization

=+ + +

Symbolization requires…

1. FEATUREFeature dimensionality -- conceptualizing the feature that is to be portrayed in terms of the extent of the phenomena

2. ATTRIBUTELevel of measurement -- selecting (and maybe changing) the level of measurement of the original data values

Four initial levels of measurement

Nominal level -- class differencesOrdinal level -- class differences and rank within classInterval level -- class differences and numerical values with an arbitrary zero valueRatio level -- class differences and numerical values with the zero value denoting absence of a feature

Reduced to Qualitative / Quantitative

Nominal level = qualitative data / information

Ordinal, interval, ratio level = quantitative or numerical data / information

Levels of measurement for cartography

Nominal qualitativeOrdinal, interval, ratio quantitative (numerical)Extensions – not in this class

Feature dimensionality (the geographic FEATURE)

0 to 3 dimensionsPoint (0-D)Line (1-D)Area (2-D)Surface (2-½)Volume (3-D)

Feature dimensionality -> spatial data models

Discrete phenomenaContinuous phenomena

Let’s look at this fromJenks’ point of view

Graphic marks (feature representation)

PointLinePolygon(Pixels, facets, etc.)

Visual variables

A reduction

QualitativeHueOrientationShapeArrangement

QuantitativeValue (Lightness)Chroma (Saturation)Spacing (Texture)Size (includes Perspective Height)

Color variables

Hue

Value / lightness

Saturation / chroma

Hue, value, saturation

Hue is the most obvious characteristic of a color Saturation is the purity of a color

High saturation colors look rich and fullLow saturation colors look dull and grayishSometimes saturation is called chroma

Value is the lightness or darkness of a color

Hue

Chroma

Value

Hue

Value

Size

Shape

Orientation of a point

Orientation of a polygon

Size

Quantitative

Arrangement

The Symbol Selection Process

Major factors underlying the symbol selection process

Level of measurementof data describing each featureof information about the feature that we want to communicate to the map reader

Spatial dimensionpoint, line, area, surface, volume

Graphic markspoint, line, area, surface (pixels, facets, etc.)

Visual variables for the different graphic marksfor the different conceived spatial structuresand for the different levels of measurement

Mapping Methods

Choropleth mapsProportional symbol mapsIsopleth mapsDot mapsDasymetric mapsPrism mapsFlow mapsCartograms