Eva's description is excellent. But I would also like to mention my favorite:
"Gemeindelexikon für das Königreich Preußen : auf Grund der Materialen der
Volkszählung vom 1. Dezember 1905 und anderer amtlicher Quellen."
This gazetteer provides the locations of Catholic and Evangelical churches
and tells where the civil records were kept. The LDS film number for
Ostpreußen and Westpreußen is 1186701.
Jerry Kattke
Naperville, Illinois, USA