Superimposed display method and superimposed display apparatus

A computer displays a plurality of edge lines extracted from a shot image of a spatial structure that has been shot by an image shooting apparatus, and a plurality of ridge lines included in a model image represented by model information of the spatial structure, in a manner such that the edge lines and the ridge lines are selectable. Then, the computer accepts a selection instruction indicating an edge line and a ridge line of an overlay target. Finally, in accordance with the accepted selection instruction, the computer displays a superimposition image in which the model image has been superimposed onto the shot image in a manner such that the edge line and the ridge line of the overlay target overlap each other.