People were often named for the town >from which they
came-but they were named that after they left. When a
person was living in eg Szlajch, everyone was from
there so it didn't help identify this Itzig (or
whatever the first name was) >from another of the same
name. He would be Dark Itzig (and become Itzig
Schwartz or Itzig Cherney when inherited surnames were
taken-Schwartz is German/Yiddish and Cherney
Polish/Russian for dark) or Itzig Berkowitz if his
father was Ber or something else.
However, when Itzig moved to the nearby town, he was
often identified as Itzig >from Szlajch, Itzig
Szlajcher, and that might become the inherited
surname. So, if the name came >from the town, Itzig
did not live there at the time-but earlier!
My 2nd gr grandfather was Joseph Schmai, who took the
inherited surname THALHEIMER in 1810. He was from
Thalheim but lived in Unterschupf where he was known
as the guy >from Thalheim. It is very handy for me to
know where to look in an earlier time period. The
other side of my family are RUSLANDERS-which leaves
all of Russia for them to have come from.