Page Layout Composition: Content Types and Columns
Although page layouts are stored in the Master Page Gallery in the root site of a site collection, the core of page layouts stems from content types, specifically publishing content types in SharePoint Server 2010. When you create page layouts, those page layouts can inherit from a page layout content type or directly from the page content type. The typical page layout model comprises (reading from left to right):
Page content type > Page layout content type > page layout > publishing page
Content types in SharePoint 2010 centrally define content (such as the associated metadata) and other functionality (such as workflow or special policies). As a result, content throughout a site collection ...