Reference works -- like encyclopedias, handbooks, and dictionaries -- provide great overviews and background information.
In short, reference works are a great way to begin your research.
Scholarly sources have a different level of authority and credibility because they have been approved by a group with recognized expertise in the field under discussion. That approval process includes many steps for verifying facts, reducing bias, and for identifying conflicts of interest. To help aid that process, authors organize and structure their scholarly work differently in order to document evidence that either supports or negates claims and conclusions.
For a Philadelphia-focus: