It is desirable that a 3D city model at level of detail 2 (LOD2) has texture images mapped on building surfaces. Texture images mapped on building surfaces are utilized not only for providing a realistic appearance but also for enabling some analyses, such as investigation of stories of a building and detection of doors and windows on a building surface. We conducted an investigation on the resolution of texture images produced from aerial nadir and oblique images. First, we set up the required resolutions for the investigation of stories and the detection of doors and windows by using simulated images of various resolutions. Next we obtained the general formula to calculate the resolution of a texture image mapped on a vertical surface. Then we conducted a numerical analysis on a texture image mapped on a vertical surface produced from a nadir image and an oblique image collected by aerial cameras popularly utilized in Japan. The results of the analysis indicate that a texture image mapped on a vertical surface produced from a nadir image collected in the usual procedure of aerial photogrammetry would be unable to satisfy the required resolution for the detection of doors and windows. On the contrary, the results indicate that a texture image mapped on a vertical surface produced from an oblique image can be utilized for not only investigation of stories but also detection of doors and windows. However, there remain some problems to solve in the utilization of an oblique image for texture mapping.