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Date: Fri, 28 Jan 2000 09:15:42 +0000
To: waphgis@u.washington.edu
From: Conor Teljeur <teljeurc@tcd.ie>
Subject: Re: Adjacencies in ArcView

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>Has anyone come across a way to get adjacency matrices
>(or simply a list of the adjacent counties for each
>county in a state) in ArcView?  I can see how to get
>this by finding them for each county one at a time, but
>am wondering if anyone has (or knows of) an Avenue Script
>(or other way) to automate it and create the set of
>adjacencies for a whole state without doing one county
>at a time.


Hi

I take it that you are using this for some sort of Bayesian analysis. We do
this regularly and use the attached script [neighbour.ave] which calculates
contiguous neighbours for all polygons in a theme. You should first put an
index field into the attributes file that identifies polygons from 1 to x.
The output will be a comma delimited textfile with x rows in order 1 to x
each containing the neighbours for that polygon. We normally open the text
file in Excel for ease of calculating the offset [cumulative number of
neighbours].

I hope this is what you were looking for,

	Conor

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Content-Type: text/plain; name="neighbour.ave"; charset="us-ascii"
Content-Disposition: attachment; filename="neighbour.ave"

'*** Export the neighbor matrix to a .txt file

theProject = av.GetProject
theView = av.GetActiveDoc
theTheme = theView.GetactiveThemes.Get(0)
theFTab = theTheme.GetFTab

'Get the name for neighbor file to export
theFN = FileDialog.Put("neighbor.txt".AsFileName, "*.txt", "Name An
Adjacency File To Write")

'Get the list of fields in FTab

numeric_fields = {} 'Numeric fields in the VTab
field_aliases = {} 'List of field aliases
all_fields = theFTab.GetFields

'Build list of numeric fields from all fields.
'Also list of field aliases to display to user.
for each f in all_fields
if (f.IsTypeNumber) then
numeric_fields.Add(f)
field_aliases.Add(f.GetAlias)
end
end

fname = MsgBox.ListAsString(field_aliases,
"Select the variable for identification:",
"Export Neighbor Matrix to a TEXT File")

if (fname <> nil) then
'Match the alias to the actual field object
theField = numeric_fields.Get(field_aliases.FindByValue(fname))
else
exit
end

' Set modified flag, clear any previous selection

av.GetProject.SetModified(true)
theFTab.GetSelection.ClearAll
theFTab.UpdateSelection

' find the total number of records

theCount = theFTab.GetNumRecords

' define an output file for storing adjacency relationship

outFile = LineFile.Make(theFN, #FILE_PERM_WRITE)

' Find out adjacent polygons for each individual polygon

theBitMap = theFTab.GetSelection

for each rec in theFTab
theIndex = theFTab.ReturnValueNumber(theField, rec)
theRecord = rec.Clone
theFTab.GetSelection.Set(theRecord)
theFTab.UpdateSelection
theFTab.SelectByFTab(theFTab, #FTAB_RELTYPE_ISWITHINDISTANCEOF,
0, #VTAB_SELTYPE_NEW)

selBitMap = theFTab.GetSelection
theString = theIndex.AsString
for each rec in selBitMap
recVal = theFTab.ReturnValue(theField, rec)
if (recval <> theIndex) then
theString = theString++recVal.AsString
end
end

' Write results to file and clear the selection

outFile.WriteElt(theString)
theFTab.GetSelection.ClearAll

end
outFile.Close



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