New Contributor
Posts: 3

# Accounting for neighboring geospatial values in SAS

I originally asked this question on Stack Overflow and Stack Exchange, going to try my luck here this time.

I'm trying to model the number of parks in a neighborhood as a function of education, land area (both continuous variables), and poverty percentage (categorical). There may be other covariates included but for the sake of the question I will exclude them for now. I chose a Poisson model because to my understanding this is the model that is ideal for count data and my data has a lot of sampling zeroes.

My unit of analysis for the neighborhood is the census tract. Using ArcGIS, I joined geocoded point information about parks to a census tract shape file, exported this information into SAS, and generated counts. I then ran the following Poisson model.

proc genmod data = parks;

class povper / descending;

model cnt = povper edu area / link=log dist=poi;

run;

My issue with this model is that it doesn't take into account the number of parks in neighboring census tracts. I've been reading about possibly creating a spatially lagged dependent variable, but according to this answer, spatial lag and poisson don't necessarily mix. All of the census tracts in my table have x/y coordinates. Does anyone have advice on how I could incorporate the park counts from neighboring census tracts into my model using SAS?

SAS Employee
Posts: 340

## Re: Accounting for neighboring geospatial values in SAS

Hi,

Have you tried PROC GLIMMIX  RANDOM statement with TYPE=SP(GAU)(x,y)  ?

New Contributor
Posts: 3

## Re: Accounting for neighboring geospatial values in SAS

Hi, I've never used the GLIMMIX statement before. What exactly does the type option represent? Thanks.

SAS Super FREQ
Posts: 3,833

## Re: Accounting for neighboring geospatial values in SAS

See this example in the PROC GLIMMIX doc:

SAS/STAT(R) 13.1 User's Guide

For lots of details, including SAS code, see Schabenberger & Gotway, Statistical Methods for Spatial Data Analysis

Statistical Methods for Spatial Data Analysis (Chapman &amp; Hall/CRC Texts in Statistical Science):...

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