For the purpose of the best possible use of orthophotomaps formed by the digital photometry, the simple method of estimating the diffuse reflectance factor by photographic density is developed and tested. First, the model for evaluating effects of film characteristics, A/D conversion, and geographical feature distorting photographic density is constructed. Elements of the geographical affection in this model are the diffuse-reflection component of direct solar insolations and scattering solar insolations, the specular-reflection component of direct solar insolations, and the compensation for evaluating the shade produced with the irregularity in meshes, such as a crown, according to an observation angle. Next, the method of utilizing the balloon, whose picture was taken in the photo, as a color collimating mark is examined. Every slope is assumed to receive as much solar insolation as a portion of the balloon with the same normal as that slope. Then, the formula that presumes a relative diffuse reflection factor corresponding to each normal vector from the photographic density distribution of the balloon is derived on the basis of the model. The density distribution of balloons computed by this method is almost equal to the photographic density distribution of actual balloons.