Interviewing stakeholders is a way to elicit information about requirements for a system-to-be. A difficulty when preparing such elicitation interviews is to select the topics to discuss, so as to avoid missing important information. Stakeholders may spontaneously share information on some topics, but remain silent on others, unless asked explicitly. We propose the Elicitation Topic Map (ETM) to help engineers in preparing interviews. ETM is a diagram showing topics that may be discussed during interviews, and shows how likely stakeholders discuss each of these topics spontaneously. If a topic is less likely to be discussed spontaneously, then this suggests that engineers may want to prepare questions on it, before the interview. ETM was produced through theoretical and empirical research. The theoretical part consisted of identifying topic sets based on a conceptual model of communication context, grounded in philosophy, artificial intelligence, and computer science. The empirical part involved interviews with requirements engineering professionals to identify the topic sets and topics in each set, surveys of business people in order to evaluate how likely they would spontaneously share information about topics, and evaluations of how likely students would share information about each topic, when asked about requirements for social network websites.