It isn't required if the shapefile is sorted correctly (in polygon order). That is, if it is sorted to use a particular variable such as BLOCKCE10. Frequently, the Census data is not sorted correctly. If you use the ID statement, then you need to specify the variables in order of how you use them. So, if you used county, tract and block, you should sort them with "ID countryfp10 tractce10 blockce10;". The map must be in order that you can view it with GMAP to be able to use it with GINSIDE. If you see lines crossing with GMAP, then GINSIDE will 'see' the map that way too. Therefore, the data would be wrong. We used an example of a Census file for the ID statement because it is wrong so often: http://support.sas.com/documentation/cdl/en/graphref/67288/HTML/default/viewer.htm#p1sz5u47czzcj2n120k9fnqeb249.htm I don't know about the documentation that isn't SAS.
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