1. NCGA GeoMath Lesson North Carolina Geographic Alliance 2014
Choropleth Map
NCGA GeoMath Lesson
North Carolina Geographic Alliance
2014

2. How can such different looking maps show the same variable?
Cartographic reasons
Different slicing values
Different levels of spatial aggregation
Geographical reasons
Uneven distribution of minorities at the state scale as well as at the national scale
Concentration of minorities in cities, particularly in northern states 2

3. Percent of Population White (not Hispanic)

4. Different ways of “slicing” data
The Data {42, 50, 55, 57, 61, 77, 79, 97}
Equal interval
Three classes based on range 40 to 100
{42, 50, 55, 57} {61, 77, 79} {97}
Quantile
Quartiles (lowest 1/4 of observations, next 1/4, …)
{42, 50} {55, 57} {61, 77} {79, 97}

5. Different ways of “slicing” data
Natural breaks
{ }
{42} {50, 55, 57, 61} {77, 79} {97}
Standard deviations
Mean = 64.75, Std. Dev. =

6. Natural Breaks

7. Equal Interval

8. Quintiles (quantiles based on division into 5 classes)

9. Quintiles
Natural Breaks
Equal Interval