Proportional symbols Flashcards
what is a proportional symbol map
depicts spatial variation in a value magnitude using proportional sized point symbols.
what are the aspatial data requirements?
can use raw or derived data
when should you not choose proportional symbol?
- range of data values is limited
- data are interval level
- data normalized by area
what is important about data range
must be adequately large so that there is a significant difference in relative symbol size
what are advantages to PS
- ease of interpretation
- ability to portray distribution of multiples
- ability to portray multiple attributes of phenomena
what are disadvantages of PS
inaccurate perception of symbol size
geometric symbols vs Mimetic symbols
geometric symbols- simplistic, abstract
Mimetic symbols- mimic the attribute, confusing?
when in doubt KIS
how should replicative symbols be scaled
by area, not by height
what are the two types of proportional symbol mapping
range graded (classified) and directly proportional, (Graduated).
what is Eddinghaus illusion
areas are perceived to be larger or smaller based on the surrounding features.
what is the flannery scaling factor
a psychological scaling factor that incorporates distortion in size perception
what is a multivariante symbol
an symbol that portrays multiple pieces of information. eg Double pie chart with stacked proportional symbol.
what are the two abstract symbol designs for overlapping
- cut out, asthetically pleasing, less accurate
- transparent, more accurate, but difficult to identify and differentiate
what design principle is the most important for proportional symbol
figure ground separation
