Oblique-angle deposition of indium tin oxide (ITO) is used to fabricate optical thin-film coatings with a porous, columnar nanostructure. Indium tin oxide is a material that is widely used in industrial applications because it is both optically transparent and electrically conductive. The ITO coatings are fabricated, using electron-beam evaporation, with a range of deposition angles between 0 degrees (normal incidence) and 80 degrees. As the deposition angle increases, we find that the porosity of the ITO film increases and the refractive index decreases. We measure the resistivity of the ITO film at each deposition angle, and find that as the porosity increases, the resistivity increases superlinearly. A new theoretical model is presented to describe the relationship between the ITO film's resistivity and its porosity. The model takes into account the columnar structure of the film, and agrees very well with the experimental data.