What is a block reference?

[CADangrybird]

What is the essence of a block reference? If it is a reference, why it will be saved as internal object of the drawing but on the other side, xref won't be saved that way? We have to bind xref into the drawing we want to send out but we don't have to do that for a block reference.  

[SeeMSixty7]

Block Definition is what defines the bock and is stored inside the drawing. (All the pieces of the block)

Block Reference is an INSERT of a block. It is pretty much just an insertion point and basic information about the Insertion of that block reference, because to display that block it looks the information up from the Block Definition, This reduces the number of actual entities in your drawing.

An External Reference is the same thing, but the definition is stored Externally in another file.

If you want an XREF-to be visiable in your file, that file needs to be available. Binding that XREF to a drawing creates an internal definition that moves the External definition to be defined internally. The Difference between BIND or INSERT is how AutoCAD brings that definition into the drawing. With unique Layer names, linetypes etcs (Basically prefixes on typical; drawing properties) or as an INSERT, Maps all those to current drawing settings.

So in short a Block Reference is looking at something already stored in the Drawing, no need to bind it.

An XREF is stored in a separate file and needs to be available to be viewed, so if you want to bind it you can or send the file along with the drawing referencing it.

Good luck and I hope that helps.

[john.uhden]

@SeeMSixty7's response is dead on.  Rather than binding xrefs, consider using ETRANSMIT which can include many other dependent files to make your submittal accurate.  I wrote that wrong... can include many other files onto which your drawing depends.

[KRyadchenko_HNTB]

How to extract the information from Block Reference?
I got a DWG from Civil Engineer looking for Tin Surface to publish to BIM 360.
But it looks like all future ground is in Block References and I can't get a surface out of it. 
I can see the contour lines, but I can't edit the Block Reference. How to get to the content of the Block Reference?

[ВeekeeCZ]

That would be a C3D object for which you don't have the Enabler installed.

If you have any follow-up questions, better post them HERE 

[Sea-Haven]

For non CIv3D user you can convert a surface to  3dfaces, this can then be used by other software, we always did this for external clients.

So go back to who you got the dwg from and ask for the 3dfaces of the surfaces. These come out on one layer per surface.