Copyright, © Qiming Zhou GEOG1150. Cartography Generalisation and Symbolisation

2  The elements of generalisation  The controls of generalisation  Classification, simplification and exaggeration manipulations  Symbolising geographical features

Generalisation and Symbolisation3 Selection and generalisation  Selection - to limit our concern to those classes of information that will serve the map’s purpose  Generalisation - to fit portrayal of selected features to the map scale and to the requirements of effective communication

Generalisation and Symbolisation4 Generalisation concepts  Classification - order, scale and group features by their attributes  Simplification - determine important characteristics of feature attributes and eliminate unwanted detail  Exaggeration - enhance or emphasise important characteristics of the attributes  Symbolisation - use graphic marks to encode the information for visualisation and place them into a map

Generalisation and Symbolisation5 The elements of generalisation  Classification Qualitative attributes Quantitative attributes  Simplification  Exaggeration E.g. 20m street on 1:100,000 map scale would be only 0.2mm wide  Symbolisation

Generalisation and Symbolisation6 Classification Classification of a point pattern. After clustering the points, the cartographer selects a position within each cluster and places a dot to “typify” the cluster. The “typical” position need not coincide with the position of any of the original data points. From Robinson, et al., 1995

Generalisation and Symbolisation7 Simplification Simplification by point elimination. In the illustrated clusters of points, one original point is selected to represent each cluster of original points on the generalised map. From Robinson, et al., 1995

Generalisation and Symbolisation8 Simplification (cont.) Reducing map scales leads to the consequent simplifications. From Robinson, et al., 1995

Generalisation and Symbolisation9 Simplification (cont.) Reducing map scales leads to the consequent simplifications. From Robinson, et al., 1995

Generalisation and Symbolisation10 Exaggeration Two representations of Great Britain and Ireland. (A) simplified to fit the scale and is suitable for a reference map intended to give the impression of detailed precision. (B) diagrammatric generalisation suitable as a base on which to display thematic data. From Robinson, et al., 1995

Generalisation and Symbolisation11 The controls of generalisation  Map purpose and conditions of use  Map scale  Quality and quantity of data  Graphic limits Physical limits Physiological and psychological limits

Generalisation and Symbolisation12 Classification manipulations  Point feature methods Collapsing Typification  Line feature typification  Aggregation of areas  Aggregation of volumes - e.g. Classification for choropleth maps

Generalisation and Symbolisation13 Collapsing Illustrations of the collapsing process in cartographic generalisation. Each feature represented in the left diagrams has lost at least one dimension in its portrayal in the right diagram. Cited in Robinson, et al., 1995

Generalisation and Symbolisation14 Representations illustrating typification by classification of point, line and area features. Cited in Robinson, et al., 1995 Typification

Generalisation and Symbolisation15 Aggregation of areas The original data area mapped at a scale of 1:X. (A) represents a smaller-scale agglomeration of the original data. (B) represents the further aggregation of areas for an even smaller-scale representation. From Robinson, et al., 1995

Generalisation and Symbolisation16  Elimination Point elimination Area elimination  Smoothing Filtering Simplification manipulations

Generalisation and Symbolisation17 Elimination Simplification accompanied by scale reduction. Since the scale is successively reduced from (A) to (E), an increasing number of points in the outline must be eliminated. After Robinson, et al., 1995

Generalisation and Symbolisation18 Elimination (cont.) Simplification applied at a constant scale. The four maps (A through D) represent increasing simplifications of the coastline and hydrography. From Robinson, et al., 1995

Generalisation and Symbolisation19 Point elimination Simplification of the outline by point elimination. The points indicated on the map to the left were retained on the map to the right where they were connected with straight-line segments. All points not selected on the map to the left were eliminated in producing the map on the right. Cited in Robinson, et al., 1995

Generalisation and Symbolisation20 Line simplification process Successive stages in line simplification process: (1) The initial line. (2) Point C, having the greatest perpendicular distance to line AB in (1) is selected for retention. Lines AC and CB are drawn. (3) The elimination of points between points A and C, because no perpendicular exceeds the threshold, and retention of point D, because its perpendicular distance to line CB does exceed the threshold. Cited in Robinson, et al., 1995

Generalisation and Symbolisation21 Area elimination Simplification by feature elimination. Areas on the left map are either shown in their entirety or completely eliminated in the feature-simplified map on the right. Cited in Robinson, et al., 1995

Generalisation and Symbolisation22 Area elimination (cont.) Simplification by area elimination. Example algorithm using size and proximity to determine which features to eliminate. Cited in Robinson, et al., 1995

Generalisation and Symbolisation23 Smoothing Examples of smoothing operators applied to linear data. Line A represents the original data. Line B: a three-term moving average with unequal weights. Line C: a five-term moving average with uneven weights. Line D: a three-term equally weighted moving average. From Robinson, et al., 1995

Generalisation and Symbolisation24 Surface fitting The shaded plane, with respect to the surface shown, is situated so as to minimise the sum of the squares of the deviations between points on the surface and corresponding points on the plane. From Robinson, et al., 1995

Generalisation and Symbolisation25 Symbolising geographical features  Point symbolisation Qualitative Quantitative  Line symbolisation Qualitative Quantitative  Area symbolisation Qualitative Quantitative

Generalisation and Symbolisation26 Qualitative point symbolisation Nominally scaled pictorial symbols on a map promoting winter activities in a portion of the state of Wisconsin. The map legend lists 14 symbols. Cited in Robinson, et al., 1995

Generalisation and Symbolisation27 Qualitative point symbolisation (cont.) Nominally scaled symbols are used to indicate four classes of climatic stations. Left: the use of orientation of symbols. Right: the use of the visual variable, shape. From Robinson, et al., 1995

Generalisation and Symbolisation28 Symbols are proportionally scaled so that areas of the symbols are in the same ratio as the population numbers they represent. From Robinson, et al., 1995 Quantitative point symbolisation

Generalisation and Symbolisation29 Quantitative point symbolisation (cont.) Left: symbols are range-graded to denote the population of the cities. Right: symbols are ordinally scaled. The legends are different due to the different levels or measurement. From Robinson, et al., 1995

Generalisation and Symbolisation30 Quantitative point symbolisation (cont.) Three legends whose symbols are identical. The added information in the form of text puts one legend on an ordinal scale, one on a range-graded scale, and one on a ratio scale. From Robinson, et al., 1995

Generalisation and Symbolisation31 Use of visual variable Symbols use the visual variable value (colour) to order the data. From Robinson, et al., 1995

Generalisation and Symbolisation32 Use of visual variable (cont.) Left: total population is symbolised by size, while percentage of black inhabitants is symbolised by the value (colour). Right: Percentage of black inhabitants is symbolised by the size, while total population is symbolised by the value (colour). From Robinson, et al., 1995

Generalisation and Symbolisation33 Qualitative line symbolisation Examples of lines of differing character (the visual variable shape) which are useful for the symbolisation of nominal linear data. From Robinson, et al., 1995

Generalisation and Symbolisation34 Ordinal portrayal The use of line width (visual variable size) enhanced by the use of line character (visual variable shape) to denote the ordinal portrayal of civil administrative boundaries. From Robinson, et al., 1995

Generalisation and Symbolisation35 Range-graded line symbols. On this map of immigrants from Europe in 1900, lines of standardised width are used to represent a specified range of numbers of immigrants. From Robinson, et al., 1995 Quantitative line symbolisation

Generalisation and Symbolisation36 Qualitative area symbolisation Some standardised symbols for indicating lithologic data as suggested by the International Geographical Union Commission on Applied Geomorphology. From Robinson, et al., 1995

Generalisation and Symbolisation37 Qualitative area symbolisation (cont.) Portrayal of North American air masses and their source regions. Although data have quantitative characteristics, the intent of this illustration is simply to portray location of air masses. This can be accomplished by using nominal area symbolisation. Cited in Robinson, et al., 1995

Generalisation and Symbolisation38 Quantitative area symbolisation Map illustrating the range-graded classification of Florida counties. The use of the visual variable value (colour) creates a stepped surface. Cited in Robinson, et al., 1995

Generalisation and Symbolisation39 Appropriate uses of the visual variables Feature Dimension Level of Measurement NominalOrdinal/Interval/Ratio QualitativeQuantitative PointHue (colour)Size shapeValue (colour) OrientationChroma (colour) LineHue (colour)Size ShapeValue (colour) OrientationChroma (colour) AreaHue (colour)Value (colour) ShapeChroma (colour) PatternSize Orientation VolumeHue (colour)Value (colour) ShapeChroma (colour) PatternSize Orientation Appropriate uses of the visual variables for symbolisation. The visual variable in italics are of secondary importance. From Robinson, et al., 1995