Proportional Symbols
True vs conceptual point data
geometric
pictographic
Scaling of symbols: Interval and ratio (sometimes ordinal = range grading)
mathematical (formulae, problems)
perceptual
Legend (nested or linear): Bar
Linear: problems with figure ground contrast
Symbolization
Transparent vs. Opaque
Overlap vs scaling and zoom
redundant symbols
Problem of unevenness of uniform area assumption
Leads to Dot and Dasymetric maps
Dasymetric maps (part isopleth, part choropleth)
Jumps allowed.
Dependent upon ancillary variables (J. K. Wright, 1936 map of Cape
Cod)
Dot maps are suitable for raw counts
Manual vs. Automated
Deciding on dot size and unit value
Nomograph (Robinson)
Dot density shading (even vs random, base on grids)
Langford & Unwin: Population Density (1994) = filtered dasymetric
map