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How can I interpret the results of Hot Spot Analysis (Getis-Ord Gi*) ?

Question asked by mli.erin1919 on May 16, 2018

Hi all,

I'm confused when interpreting the results of hot spot analysis generated with ArcGIS 10.4.


The data I'm working with are 70 tree plots, each plot has around 100 trees. These trees have an attribute, let's call it as A, measured repeatedly from 2014 to 2016. What I'm trying to do is to find out the hot spots as well as the cold spots in terms of the attribute A for all of these 70 plots one by one. Also, I'll do the same thing for 3 years data to get an idea about how hot or cold spots vary during 3 years within one plot.


Now let's see one plot of them. I did Hot Spot Analysis on the attribute A for 2014, 2015 and 2016, and get quite various results, especially the results of the year 2015 were quite different from the other two years (see Fig.2014, 2015, 2016). Then I checked data in 2015, and found that the dots being "not significant" in 2015 but being hot spots in 2014 and 2016 all had relatively high value of attribute A (see Fig2015_selected & Screenshot_of_attribute). Should they be hot spots just like 2014 and 2016 as well? Why they were not significant although located close to each other and having high attribute values? I redid the analysis several times, to make sure there were not errors generated by accident. 


I also did the global Moran I analysis for this plot with 2015 data, get the results I = 0.1, z-score = 2.9, p < 0.05, indicating a significantly clustered pattern. I did local Moran I analysis too, the result is in Fig.2015_LocalMoranI, still not getting clustered high values. 


So, I'm so confused. I read documents on Esri website but did not get answers to this. 


I appreciate any help here! Thanks a lot!