Generate Spatial Weights Matrix (Spatial Statistics)
Summary
Constructs a spatial weights matrix (.swm) file to represent the spatial relationships among features in a dataset.
Illustration
Usage

Output from this tool is a spatial weights matrix file (.swm). Tools that require you to specify a Conceptualization of Spatial Relationships option will accept a spatial weights matrix file; select GET_SPATIAL_WEIGHTS_FROM_FILE for the Conceptualization of Spatial Relationships parameter and, for the Weights Matrix File parameter, specify the full pathname to the spatial weights file you create using this tool.
This tool also reports characteristics of the resultant spatial weights matrix file: number of features, connectivity, minimum, maximum and average number of neighbors. This summary is accessible from the Results window and may be viewed by rightclicking on the Messages entry in the Results window and selecting View. Using this summary, ensure that all features have at least 1 neighbor (8 neighbors is ideal). In general, especially with large datasets, a low value for feature connectivity is desirable.

Whenever using a distancebased Conceptualization of Spatial Relationships, data should be in a Projected Coordinate System (rather than a Geographic Coordinate System).

For line and polygon features, feature centroids are used in distance computations. For multipoints, polylines, or polygons with multiple parts, the centroid is computed using the weighted mean center of all feature parts. The weighting for point features is 1, for line features is length, and for polygon features is area.

The Unique ID field is linked to feature relationships derived from running this tool. Consequently, the Unique ID values must be unique for every feature and typically should be in a permanent field that remains with the feature class. If you don't have a Unique ID field, you can easily create one by adding a new integer field to your feature class table and calculating the field values to be equal to the FID/OID field. You cannot use the FID/OID field directly for the Unique ID parameter.

The polygon contiguity options, CONTIGUITY_EDGES_ONLY and CONTIGUITY_EDGES_CORNERS, for the Conceptualization of Spatial Relationships parameter are only valid for polygon features. These options are available with the ArcInfo license only.

The Number of Neighbors parameter may override the Threshold Distance parameter for Inverse or Fixed Distance Conceptualizations of Spatial Relationships. If you specify a threshold distance of 10 miles and 3 for the number of neighbors, all features will receive a minimum of 3 neighbors even if the threshold has to be increased to find them. The threshold distance is only increased in those cases where the minimum number of neighbors is not met.
The CONVERT_TABLE option for the Conceptualization of Spatial Relationships parameter may be used to convert an ASCII spatial weights matrix file to a .swm formatted spatial weights matrix file. First you will need to put your ASCII weights into a formatted table (using Excel, for example).
Caution:If your table includes weights for selfpotential, they will be omitted from the .swm output file, and the default selfpotential value will be used in analyses. The default selfpotential value for the Hot_Spot_Analysis tool is one, but this value can be overwritten by specifying a SelfPotential Field value; for all other tools, the default selfpotential value is zero.
For polygon features, you will almost always want to choose Row for the Standardization parameter. Row Standardization mitigates bias when the number of neighbors each feature has is a function of the aggregation scheme or sampling process, rather than reflecting the actual spatial distribution of the variable you are analyzing.

The Modeling Spatial Relationships help topic provides additional information about this tool's parameters.
When using shapefiles, keep in mind that they cannot store null values. Tools or other procedures that create shapefiles from nonshapefile inputs may store or interpret null values as zero. This can lead to unexpected results. See also Geoprocessing considerations for shapefile output.
Syntax
Parameter  Explanation  Data Type 
Input_Feature_Class 
The feature class for which spatial relationships of features will be assessed.  Feature Class 
Unique_ID_Field 
An integer field containing a different value for every feature in the Input Feature Class.  Field 
Output_Spatial_Weights_Matrix_File 
The full pathname for the spatial weights matrix file (.swm) you want to create.  File 
Conceptualization_of_Spatial_Relationships 
Specifies how spatial relationships among features are conceptualized.
Note: Polygon Contiguity methods are only available with an ArcInfo license.  String 
Distance_Method 
Specifies how distances are calculated from each feature to neighboring features.
 String 
Exponent (Optional) 
Parameter for inverse distance calculation. Typical values are 1 or 2.  Double 
Threshold_Distance (Optional) 
Specifies a cutoff distance for Inverse Distance and Fixed Distance conceptualizations of spatial relationships. Enter this value using the units specified in the environment output coordinate system. A value of zero indicates that no threshold distance is applied. When this parameter is left blank, a default threshold value is computed based on output feature class extent and the number of features.  Double 
Number_of_Neighbors (Optional) 
An integer reflecting either the minimum or the exact number of neighbors. For K Nearest Neighbors, each feature will have exactly this specified number of neighbors. For Inverse Distance or Fixed Distance each feature will have at least this many neighbors (the threshold distance will be temporarily extended to ensure this many neighbors, if necessary). When there are island polygons and one of the Contiguity Conceptualizations of Spatial Relationships is selected, then this specified number of nearest polygons will be associated with those island polygons.  Integer 
Row_Standardization (Optional) 
Row standardization is recommended whenever feature distribution is potentially biased due to sampling design or to an imposed aggregation scheme.
 Boolean 
Input_Table (Optional) 
A table containing numeric weights relating every feature to every other feature in the input feature class. Required fields are the Input Feature Class Unique ID field, NID (neighbor ID), and WEIGHT.  File 
Code Sample
The following Python Window script demonstrates how to use the GenerateSpatialWeightsMatrix tool.
import arcpy arcpy.env.workspace = "C:/data" arcpy.GenerateSpatialWeightsMatrix_stats("911Count.shp", "MYID","euclidean6Neighs.swm","K_NEAREST_NEIGHBORS","#", "#", "#", 6,"NO_STANDARDIZATION")
The following standalone Python script demonstrates how to use the GenerateSpatialWeightsMatrix tool.
# Analyze the spatial distribution of 911 calls in a metropolitan area # using the HotSpot Analysis Tool (Local Gi*) # Import system modules import arcpy # Set geoprocessor object property to overwrite existing output, by default arcpy.gp.overwriteOutput = True # Local variables... workspace = "C:/Data" try: # Set the current workspace (to avoid having to specify the full path to the feature classes each time) arcpy.env.workspace = workspace # Copy the input feature class and integrate the points to snap # together at 500 feet # Process: Copy Features and Integrate cf = arcpy.CopyFeatures_management("911Calls.shp", "911Copied.shp", "#", 0, 0, 0) integrate = arcpy.Integrate_management("911Copied.shp #", "500 Feet") # Use Collect Events to count the number of calls at each location # Process: Collect Events ce = arcpy.CollectEvents_stats("911Copied.shp", "911Count.shp", "Count", "#") # Add a unique ID field to the count feature class # Process: Add Field and Calculate Field af = arcpy.AddField_management("911Count.shp", "MyID", "LONG", "#", "#", "#", "#", "NON_NULLABLE", "NON_REQUIRED", "#", "911Count.shp") cf = arcpy.CalculateField_management("911Count.shp", "MyID", "[FID]", "VB") # Create Spatial Weights Matrix for Calculations # Process: Generate Spatial Weights Matrix... swm = arcpy.GenerateSpatialWeightsMatrix_stats("911Count.shp", "MYID", "euclidean6Neighs.swm", "K_NEAREST_NEIGHBORS", "#", "#", "#", 6, "NO_STANDARDIZATION") # Hot Spot Analysis of 911 Calls # Process: Hot Spot Analysis (GetisOrd Gi*) hs = arcpy.HotSpots_stats("911Count.shp", "ICOUNT", "911HotSpots.shp", "GET_SPATIAL_WEIGHTS_FROM_FILE", "EUCLIDEAN_DISTANCE", "NONE", "#", "#", "euclidean6Neighs.swm") except: # If an error occurred when running the tool, print out the error message. print arcpy.GetMessages()
Environments
 Output Coordinate System
Feature geometry is projected to the Output Coordinate System prior to analysis.