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At its simplest level of representation, spatial data exists as points, lines, areas, or rasters. You encode meaning into these basic shapes through a process of symbolization. Symbols allow you to illustrate a unique difference between features, some difference in magnitude between features, or another characteristic. Symbolization can take on a range of functions on a map but should be clear, concise, and easily understood by the user. In many ways, symbolization can be regarded as the coding of map features to communicate meaning.

The following diagram sets out a range of ways in which you can modify the symbolization of a feature to give it different meaning.

Visual variablePointLinearAreal2.5DTrue 3D


Spacing: point
Spacing: linear
Spacing: areal
Spacing: 2.5D
Spacing: True 3D


Size: point
Size: linear
Size: areal
Size: 2.5D
Size: 3D

Perspective height

Height: point
Height: linear
Height: areal
Height: 2.5D

Not possible


Orientation: point
Orientation: linear
Orientation: areal

Not recommended

Orientation: 3D


Shape: point
Shape: linear
Shape: areal

Not recommended

Shape: 3D


Arrangement: point
Arrangement: linear
Arrangement: areal

Not recommended

Arrangement: 3D


Value: point
Value: linear
Value: areal
Value: 2.5D
Value: 3D


Hue: point
Hue: linear
Hue: areal
Hue: 2.5D
Hue: 3D


Lightness: point
Lightness: linear
Lightness: areal
Lightness: 2.5D
Lightness: 3D


Saturation: point
Saturation: linear
Saturation: areal
Saturation: 2.5D
Saturation: 3D

Show qualitative and quantitative differences

Making sensible choices about how to represent your features to convey just the right message is key to making your map communicate effectively. For instance, if you want to show how cities (represented by point symbols) differ in their population size you would probably choose to change the size of the symbol used to represent the points. Larger symbols represent larger magnitudes and this is how our eyes and brains process the meaning of a large symbol compared to a smaller one. In another example, if you wanted to show the difference between a railroad and a freeway, changing the size (thickness) of the line isn't going to immediately show that difference. Instead, you would probably change the shape of the line to show a difference between the two features.

Assigning meaning to symbols generally means deciding whether you're showing a quantitative or a qualitative difference, that is, a difference in size or type. The following table gives some advice on the recommended ways in which you should modify your features depending on feature type and what you are trying to show. Some methods are preferable to others.



Preferred: hue, shape

Less preferred: orientation, arrangement

Preferred: size, value, lightness

Less preferred: perspective height, size


Preferred: hue, shape

Less preferred: arrangement

Preferred: size, spacing

Less preferred: perspective height, value, lightness


Preferred: hue, shape

Less preferred: orientation, arrangement

Preferred: value, lightness, saturation, size

Less preferred: perspective height, hue


None recommended

Preferred: perspective height, lightness, value

Less preferred: saturation


Preferred: orientation, arrangement, shape

Less preferred: hue

Preferred: lightness, value, saturation

Less preferred: size, spacing

Qualitative and quantitative ways of comparing features

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