Biztalk Business Rule Engine Question:

The mapper grid plays a critical role in the definition of maps, containing the links and functoids that control how data in a source instance message is transformed into an instance message that conforms to the destination schema.
The grid view can have multiple layers, called grid pages, allowing you to organize complex maps into logical subdivisions of mappings. BizTalk 2010 no longer has the limitation of 20 grid pages that exist in the previous versions of the product.