A survey is a way of collecting information about the views of the whole community or group in which you are interested. A survey may be the best choice wthen:
You need a quick and efficient way of getting information
You need to reach a large number of people
You need statistically valid information about a large number of people
The information you need isn't readily available through other means
The information you need may be obtained through other means, such as informal unstructured conversation that takes place in the course of another activity; census figures; meeting with people in the community; interviews; or observation.
See details in: http://ctb.ku.edu/en/table-of-contents/assessment/assessing-community-needs-and-resources/conduct-surveys/main