Geographers often interview people to gather information on beliefs and attitudes. how can geographers gather information without interviewing the entire population?

Observational method.

Explanation:

This method is used to collect data at first hand and to derive facts and information from the general public without interviewing them in their natural settings. Other methods can be either conducting surveys or mailed questionnaires, so geographers don't need to go to every person  and ask for their opinion they can just analyze trends in the market like the demand and supply of raw materials, labour and any other product they also make use of the statistical techniques and evaluate the present on the basis of past and future on the on present scenario.