Point Symbol Mapping

Proportional Symbols

True vs conceptual point data

Scaling of symbols: Interval and ratio (sometimes ordinal = range grading)
mathematical (formulae, problems)

Legend (nested or linear): Bar
Linear: problems with figure ground contrast

Transparent vs. Opaque
Overlap vs scaling and zoom
redundant symbols

Dot Mapping

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