A point in a topology layer represents a point feature (e.g., a fire hydrant) from a Bentley Map project or a design file. A point may have database linkages associated with it and can be loaded into a topology layer from any of the following MicroStation elements:

• text node

• zero length line string

• cell

• text

A line in a topology layer represents a linear feature (e.g., a road) from a Bentley Map project or a design file. A line may have database linkages associated with it and can be loaded into a topology layer from any of the following MicroStation elements:

• line

• line string

• curve

• arc

• complex chain

A centroid is a point feature that is inside an area. Centroids in topology layers distinguish area features from void space (e.g., the hole of a donut). A centroid may have database linkages associated with it and is typically loaded into a topology layer with boundaries.

A boundary is a line that delineates the edge of an area, such as the boundary of a land parcel or the edge of a lake. A boundary may have database linkages associated with it and is typically loaded into a topology layer with centroids.

An area in a topology layer may be inferred from a set of closed boundaries having a contained centroid or be represented by a simple or complex shape. Areas may be loaded into a topology layer from point and line features or from shape elements. However, shape elements have the restriction that common edges are exactly superimposed; i.e. all edge vertices are exactly the same.