The geography data type provides numerous built-in methods you can use to create new geography instances based on existing instances.
Creating New geography Instances
To create a buffer around a geography
STBuffer (geography Data Type)
To create a buffer around a geography, allowing for a tolerance
BufferWithTolerance (geography Data Type)
To create a geography from the intersection of two geography instances
STIntersection (geography Data Type)
To create a geography from the union of two geography instances
STUnion (geography Data Type)
To create a geography from the points where one geography does not overlap another
STDifference (geography Data Type)
Concepts
Designing and Implementing Spatial Storage (Database Engine)
Other Resources
Working with Spatial Data (Database Engine)
Help and Information
Getting SQL Server 2008 Assistance