Frankl et al 14 Present and Absent: Exploring the Holocaust of Jews in Prague Using a Mobile Application GI_Forum 2020, Issue 2 Page: 14 - 28 Full Paper Corresponding Author: frankl@mua.cas.cz DOI: 10.1553/giscience2020_02_s14 Michal Frankl 1 , Petr Mazánek 2 , Aneta Plzáková 3 , Wolfgang Schellenbacher 1 , Zuzana Schreiberová 4 and Luboš Světík 2 1 Masaryk Institute and Archives of the Czech Academy of Sciences, Czech Republic 2 Deep Vision, Czech Republic 3 Terezín Initiative Institute, Czech Republic 4 Multicultural Center Prague, Czech Republic Abstract This paper discusses the goals, methodology and experience gained in the project ‘Integration and Segregation in Cityspace: The History of the Holocaust in Prague Through a Web Application’, funded by the Technology Agency of the Czech Republic. Using a mobile application, the project aims to overlay the current cityscape with extensive datasets on the Holocaust victims who were living in Prague before their deportation. By giving insights into working with the data, and by presenting the digitized material used and the technical development of the web application, the paper also hopes to contribute to future approaches for archival and educational GIS-based applications. Following an introduction to the spatial history of Jews in Prague, the article analyses the challenges at the crossroads of documentation and digitization, technology and user interface, as well as user interaction with data. Keywords: Holocaust, Prague, mobile application 1 Introduction Due to the rapid exclusion, disenfranchisement and expulsion of Austrian Jews following the Anschluss of Austria to the German Reich, Ernst (Arnošt) Löwit, an Austrian bank assistant born in 1889, was forced to flee from Vienna to Prague in July 1938. He rented a room in Čermákova 9 in Královské Vinohrady / Königliche Weinberge, a middle-class neighbourhood, and became dependent on the support of the Jewish Community in Prague. Following the occupation of Czechoslovakia in March 1939, he tried in vain to prepare his further emigration to Shanghai. In 1941, he received a summons for a transport from Prague. Ernst Löwit was arrested on 18 October 1941 in a café on Charles Square in Prague: he had removed his Star of David to meet his non-Jewish fiancée Ludmilla Klimt and bid her farewell. Showing the