What is the difference, or intended purpose of these two object that represent the same Geography datatype in a Microsoft SQL Database?
They can't be cast between each other, but
SqlGeography has additional command when it comes to creating points, polygons etc.
I'm thinking that
System.Data.Entity is for use with Entity Framework only, whilst
Microsoft.SqlServer is for use when using the
SqlCommand directly instead?
You're right, in essence it is that simple. DbGeography is just a dumbed down version of SqlGeography, designed to work within the Entity Framework. The most popular methods of SqlGeography have been implemented within it but as you rightly point out, not all.
Whilst the two types cannot be directly cast between each other, the process of converting them is relatively simple in times where the additional functionality of SqlGeography is required.
SqlGeography geog1 = SqlGeography.STPolyFromText('<coords>', srid); SqlGeography geog2; DbGeography dbGeog; // SqlGeography to DbGeography dbGeog = DbGeography.FromText(geog1.ToString(), srid); // DbGeography to SqlGeography geog2 = SqlGeography.Parse(dbGeog.AsText());