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.
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)