1.1 Basic Mapping

Common map classifications include the Quantile Map, Natural Breaks Map, and Equal Intervals Map. Specialized classifications that are designed to bring out extreme values include the Percentile Map, Box Map (with two options for the hinge), and the Standard Deviation Map. The methods of map classification calculate a corresponding breakpoint list for a selected variable. For more information about the map classification, please read http://geodacenter.github.io/workbook/6a_local_auto/lab6a.html.

1. Natural Breaks

Natural Breaks calculates a list of breakpoints based on the fracture principle of maximum similarity within a group.

natural_breaks()

Synopsis

float[] natural_breaks(numeric, integer)

Example

SELECT natural_breaks(hr60, 5) FROM natregimes;

                    natural_breaks                     
-------------------------------------------------------
 {3.3308906802,7.4689850396,13.450747147,31.426775613}
(1 row)

2. Quantile Breaks

Quantile Breaks is based on sorted values for a variable that are then grouped into bins that each have the same number of observations, the so-called quantiles.

quantile_breaks()

Synopsis

float[] quantile_breaks(numeric, integer)

Example

SELECT quantile_breaks(hr60, 5) FROM natregimes;

               quantile_breaks               
---------------------------------------------
 {0,1.7654960252,4.06106847805,7.9740054575}
(1 row)

3. Percentile Breaks

Percentile Breaks divides the data into six ranges: the lowest 1%, 1-10%, 10-50%, 50-90%, 90-99% and the top 1%..

quantile_breaks()

Synopsis

float[] percentile_breaks(numeric)

Example

SELECT percentile_breaks(hr60) FROM natregimes;

               percentile_breaks               
-----------------------------------------------
 {0,0,2.7833299411,11.274974068,24.8236821873}
(1 row)

4. Hinge Box Breaks

Hinge Box Breaks calculates a list of breakpoints, including the top, bottom, median, and two quartiles of the data. The hinge values can be 1.5 or 3.0.

hinge15_breaks()

Synopsis

float[] hinge15_breaks(numeric)

Example

SELECT hinge15_breaks(hr60) FROM natregimes;

                        hinge15_breaks                        
--------------------------------------------------------------
 {-10.32795220545,0,2.7833299411,6.8853014703,17.21325367575}
(1 row)

hinge30_breaks()

Synopsis

float[] hinge30_breaks(anyelement)

Example

SELECT hinge30_breaks(hr60) FROM natregimes;

                       hinge30_breaks                       
------------------------------------------------------------
 {-20.6559044109,0,2.7833299411,6.8853014703,27.5412058812}
(1 row)

5. Standard Deviation Breaks

Standard Deviation Breaks calculates the number of standard deviational units of the range from lowest to highest, returning a breakpoint list.

stddev_breaks()

Synopsis

float[] stddev_breaks(anyelement)

Example

SELECT stddev_breaks(hr60) FROM natregimes;

                                      stddev_breaks                                      
-----------------------------------------------------------------------------------------
 {-6.79536838828887,-1.14564656029265,4.50407526770356,10.1537970956998,15.803518923696}
(1 row)