Contribution element to file size

Bruno Pieters said:

Is there a way to know, which element contributes the most to the file size?

Primitive elements (e.g. line-string, ellipse) have a fixed size, depending on the amount of data they contain.  An ellipse, for example, has a small number of geometric properties but a line-string can have up to 5,000 vertices.

More complex elements (e.g. cells) have a variable size, depending on the number of components of that cell.

Those elements are contained in a DGN model.  A DGN model is contained in a DGN file, which may contain many models, each of which contributes to the DGN file size.

There is no definitive answer to your question.  What do you hope to achieve?

Let's say, I received a file, that after compressing, is still heavy. I want to reduce it by deleting elements. Can I determine beforehand which element is the heaviest?

Rather than trying to find elements that are heaviest, wouldn't it be more important to only remove elements that aren't needed?

You can see the size of elements by bringing up the properties window, selecting an element and expanding the "Raw Data" section. There is a size entry in there. I think it's in bytes but i'm not sure.

Here's a line string with 2 segments:

Here's a line string with 7

But if I had drawn the 7 segment line as 7 separate single lines the overall size of those 7 elements would be larger than the single 7 segment line.

You might check if there are raster images embedded in the file, those can be very large.

There was similar discussion -  Is it possible to estimate file size as per the elements in MVBA 

In your case I would try to copy visible elements to new file and check if it has same file size. There may be some orphaned non-graphics data which takes most of the file size. 

Not directly answering your question, but did you try Data Cleanup to see if any duplication. In addition you mention compressing but did you try the Compress Options to see if these helped reducing the size.