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We present the spmat command for creating, managing, and storing spatial-weighting matrices, which are used to model interactions between spatial or more generally cross-sectional units. spmat can store spatial-weighting matrices in a general and banded form. We illustrate the use of the spmat command and discuss some of the underlying issues by using United States county and postal-code-level data.
Drukker et al. (Mon,) studied this question.