I've been working with the same problem..trying to replicate "Jenks-Fisher Natural Breaks" via SAS. The goal of the Jenks algorithm is straightforward...create N groups out of a single variable so that the within subclass variation is minimized and between class variation is maximized. It's pretty much the default classification mode for most GIS/mapping software. I'm not at all sure what tweaks ESRI has in their ArcMap..they claim their soln. is proprietary. But you can come very close to what ArcMap provides using either FASTCLUS (several times if you want to try, say, 4 through 7 different categories) or using CLUSTER and then Proc Tree. When i've done very simple checks - ie looking at the within group variance with, say, 4 categories out of ArcMap / Jenks and maxclusters = 4 with SAS. the SAS intervals have slightly less overall variance than the similar categories out of ArcMap. The data happens to be the % of quartz by weight in topsoil samples in a new USGS geochemical/mineralogical survey of the lower 48. ArcMap DOES let you start w/ any of several different categorization methods and then modify it interactively w/ a data histogram. proc fastclus data=A_Quartzn out=quartz.fastout maxclusters = 4; var A_Quartzn; run; first is proc means using the groups/clusters picked by FASTCLUS, next is the same using the 4 Jenks categories out of ArcMap. The Min/Max are the lower and upper level of each interval. Analysis Variable : A_Quartzn N Cluster Obs Minimum Maximum Mean Std Dev Variance ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ 1 703 77.7 99.9 88.7069701 6.5550437 42.9685981 2 1541 50.1 77.6 61.5883193 7.8154812 61.0817466 3 1967 22.5 50.0 38.0440773 7.7738989 60.4335038 4 591 0.2 22.4 12.0318105 6.7539344 45.6156304 ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ L:\AHS646_Bob\USGS\usgs_sas\ahs_USGS_14_09_29.sas 19:25 Wednesday, October 1, 2014 5 Modifying USGS geochemical database, Getting mapping levels The MEANS Procedure Analysis Variable : A_Quartzn N ArcMap Obs Minimum Maximum Mean Std Dev Variance ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ 1 841 73.7 99.9 86.5820452 7.6916868 59.1620463 2 1348 50.8 73.6 60.5956231 6.5572610 42.9976720 3 1687 29.0 50.7 40.8642561 6.1089930 37.3197952 4 926 0.2 28.9 17.0363931 8.6349186 74.5618201
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