An inspection apparatus determines information indicative of structure that may be hidden behind an obscuring boundary, such as a wall. A processor collects measurements of properties characterizing the hidden structure and measurements of location of the apparatus. The collected data are mapped to produce an image of intensity in the characteristic measurements. Each intensity value in the image reflects a measure of density, of material type, or of some other specific information by which hidden structure can be discerned. The intensity changes indicating the hidden structure are displayed to a user via color-coded pixels or the like.