GoranS

Spatial Autocorrelation for Rasters?

Discussion created by GoranS on Feb 26, 2015
Latest reply on Mar 2, 2015 by Dan_Patterson

Hi!

 

I wounder if it's possible to use Global Moran's I (spatial autocorrelation tool) on a pointlayer which is the result from a raster to point operation? I mean ofcourse it's _possible_ but is the result valid?

 

The reason I ask is because I get ridiculus high z-scores and wounder if I can really trust the results. I have searched to my best ability but no definite answear. I have found others recommending the raster to point operation.

 

My question is hence: can spatial autocorrelation be used on a raster (the points resulting in a raster to point)? Is that a correct way to use the tool or will the placement and amount of points disrupt the result?

 

 

About my data:

I have a shapefile with reported movementspath which are quite intricate polylines with overlaps of the own line and large differences in how large network each respondent have reported. The lines/respondents are divided in two groups (A & B).

I have made a density raster of for each group (both with the density tool and by counting the lines without respect to their lenght within radius (using spatial join & fishnet).

Then I have indexed the groups in respect to population and subtracted one from the other resulting in a index scale from -1 to +1 (in reality -0,20 to +0,29).

The pattern is very clear and give several intresting thesis and thoughts. However now I want to make sure the differences I see are statistically significant.

 

I have used Global Moran's I as well as Hot Spot (Getis-ord Gi) and cluster analysis (Anselin Local Moran's I)

All result in high significance. The z-score for Global Moran's I vary between 165 and 265 depending on the radius of the distance threshold (10 to 100 meter)(for one of the density layers, the others give similar results). Moran's vary between 0,36 and 0,07 for the same.

 

 

 

Grateful for any help!

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