[postgis-users] Create Voronoi Diagrams

[ΑΠΟΣΤΟΛΟΣ ΛΕΛΕΝΤΖΗΣ]

Hello everybody

For another time, i ask your help and your experience!!
Specifically, i want to create voronoi diagrams with postgis, and i found
the following intersting link
http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut02
So, i have installed the pl/r language and i have run the voronoi function.
But, i don't understand what kind of my data i have to place, at the below
line code
WHERE town = ''BOSTON'' AND grades LIKE ''%3%'' AND type = ''PUB''
why the writer use a WHERE statement ??
what does mean the variable "%3%" ??

Thankss
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