“The Viennese were standing and laughing. ‘Finally they got the Jews out!’ ” Ms. Ungar, who was born Mina Tepper and was one of only 36 from that transport to survive the war, recounted in video testimony. “We scraped the ice from the windows — we were so thirsty. We didn’t have water. We didn’t have anything,” she said of the train journey.

Her journey across a wintry Europe can now be traced on a database that documents about 1,100 transports, searchable by train (or boat or bus) or victim’s name. A project of Yad Vashem, Israel’s Holocaust memorial and research center, the database sheds new light on the cross-border, Europewide nature of the stages leading to the mass extermination of some six million Jews, known in Hebrew as the Shoah.

“Very often people think of the Shoah as something that took place in the camps and killing sites in Eastern Europe from a geographical perspective,” said Joel Zisenwine, who has directed the “Transports to Extinction” project since 2008. “By focusing on the transports, I think we provide a more precise image of the Final Solution,” he said. “This is a continental enterprise, if that is the right word.”

The database first went online in 2010, but Yad Vashem is promoting it now in connection with Israel’s annual Holocaust Remembrance Day on Thursday, because it has amassed enough information to map most of the deportations from Western and Central Europe. Dr. Zisenwine said the research illuminated how railroad companies and the local government authorities were complicit in the transports, and how many of them ordinary people saw.