The questionnaire could be a postal questionnaire, group questionnaire or a reply stub. Which method you choose depends on what the aim of the enquiry is and the resources available. An advantage of the questionnaire compared to the interview is that it can reach many simultaneously – conducting interviews with the same number of people would require significantly more time. In a questionnaire the respondents could be anonymous, which renders follow-ups impossible if an answer need elaboration or explanation. The interview has an obvious advantage there.
Consultation is when a certain group is asked specific questions in the planning process. It can be both experts and stakeholders and methods vary from easy questionears to more sophisticated tools such as the English system Spaceshaper.