DGN is a legacy vector format originally used with Intergraph and Bentley Microstation GIS products. It is a true beast of a CAD-oriented format that should be used for interchange only when there is no possibility of using a better format.
DGN files can contain splines, which will be imported (if possible) into curved segments. Z values will also automatically be imported.
To import from DGN format:
Choose File-Import from the main menu.
In the Import dialog browse to the folder containing data of interest.
Double-click the .dgn file desired.
Tables and drawings and other components, such as labels, will be created.
Clicking on the wasbgd.dgn file for the file folder shown above will result in the creation of two tables, two drawings, a labels component and a map.
After opening the map we move the labels layer above the drawing layer and then we color the drawing layer with lighter colors using Style to make the labels more visible.
DGN files do not provide projection information. They are more CAD files than geospatial files and are a really poor choice for the publication of spatial data.
Assume that projection information will not be captured when importing a DGN. We should try to find any information that accompanied a DGN file that may describe the intended projection so we can launch Assign Initial Coordinate System in the Component pane to specify the intended projection.
DGN may be imported in cases where the .dgn is not "broken" (to use Bentley's terminology). In cases of "broken" .dgn files, importing a .dgn may show elements in the Manifold drawing that were recently deleted in MicroStation before saving the .dgn.
DGN is thinly documented and can include format variations that are not at all documented. Although the Manifold .dgn dataport works surprisingly well across a wide range of .dgn files it is always possible that a .dgn may be encountered that cannot be imported.
An option in such cases is to use Manifold's GDAL/OGR dataport to attempt to import the .dgn through GDAL.