Here is your answer.
Let me first tell you what a survey is. It is a method to collect information of people and their lifestyle. In a survey, a person asks some questions from a specific group of people and then prepares the data according to it. One of the most famous examples of survey is census. It collects information on the population and literacy rate of a country. Similarly, government and big companies get information on the choices people make.
A survey is important for the historian to get information on the past. For instance, if a historian wants to know about the people living at a place 100 years back, he/she would go to that place and ask the locals about the past and history of that particular place.
Hope you have got your answer.