Read SparseMap to determine whether the field map is not a simple reflection of the underlying dataset. The TCustomDBGrid sets SparseMap when it builds the field map. SparseMap is false if the TCustomDBGrid builds a default field map directly from the dataset. Any changes to the field components associated with each column cause TCustomDBGrid to change SparseMap to true. When SparseMap is true, the field map may contain undefined fields if the column attributes indicate an invalid field name or an unassigned field component. 

AddMapping 

Fields