Choropleth Flashcards
Choropleth etymology
Choros = place + Plethein = To fill
AKA area mapping/shaded mapping
Choropleth definition
A map in which enumeration units are shaded with intensity proportional to data values
Enumeration Unit limits
Variation across units is not portrayed (aggregation/generalization)
Boundaries are arbitrary
Alternatives to choropleth
Dasymetric Map (Isopleth + Choropleth)
ie KDE
Ancillary variables
limiting/barrier variables like ponds
Data considerations
No raw data!
Use standardized data (ratio) because of different size enumeration units
Equal Interval classification
Each class occupies an equal range
Number of observations varies per interval
Can have a range with no observations
Makes continuous legend
Data range/ # of classes
Equal Frequency/Quantile classification
Number of observations per class are the same
Best for even distributions
Bad for odd number of observations
Bad for greatly varied enumeration unit sizes
Mean-Standard Deviation classification
bell curve
each class is the average then +/- the standard deviation
Natural Breaks/ Jenks classification
Eye test
Arbitrary class breaks
Difficult for comparison to other classifications
Can create wide class ranges
Can be misleading on frequencies due to arbitrary class breaks
Continuous Range Grading
No gaps between class ranges
1-10,11-20,21-30, ect
Non-Continuous Range Grading
Gaps between class ranges
1-10, 15-23, 30-40
Qualitative color scheme (classes)
Non-ordered, different hues
Yellow for corn
Blue for water
Sequential color scheme (classes)
Variations in lightness to represent ordered data
that blue color ramp for census maps
Diverging color scheme (clases)
Emphasize both highs and lows
For data with a 0 point in the middle, so negative and positive values
