The program 3DField can overlay a contour map on bitmap base map. One
can generate a list of bmp-files from which to choose a background. Base maps can be
combined with contour map and scaled together.
The Objects - > Base Map menu opens the dialog.

The Add button adds a file in the list. The list can
contain positions in the same file, but at other location on a map. Delete
removes a selected line from the list. Visible places or deletes the
background image from a map. Set as Default automatically places the image on
a new map. Rename gives a position a new name.
The background can be stretched to a full window, placed at the center
or adhered to two coordinate points with the Assigning Coordinates button.

Double-click (or to enter manually) two points. Each point is a pixel
location (Pixel X, Pixel Y) associated with map coordinates X, Y. One can correct both
pixel and coordinate values.