3

So I am trying to figure out how to understand the Getis Ord results from pysal.

I have a geographically enabled datatframe, and I want to figure out how to find both hot and cold spots from the results.

import pysal


fc = r"C:\temp\towns.shp"
field = "TOTALPOP10"
sdf_poly = SpatialDataFrame.from_featureclass(fc) # polygon

permutationsValue = 999
w_poly = pysal.weights.Queen.from_dataframe(df=sdf_poly, geom_col='SHAPE')
y = sdf_poly[field]
statistics_g = G_Local(y, w_poly,
                     star=True, transform='R', permutations=permutationsValue)

This all works fine and well, now I need to find significant values:

sig = statistics_g.p_sim<0.05
statistics_g.p_sim[sig]

Are these the hots zones?

If so, how do I find the cold spots as well?

2

To determine hotspots and coldspots, you first need to see globally if there exists some form of autocorrelation/clustering (Global Moran's I).

Then, you could do local statistics to determine local clusters like you did above.

  1. To determine hotspots: Low p-values (significant) areas with Positive z-scores.
  2. To determine coldspots: Low p-values (significant) areas with negative z-scores.

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