The problem to image around a corner for objects that are invisible from direct line-of-sight is intriguing as its solution may provide the basis for new methods in various fields. However, most current researches are based on back-projectionrelated methods, of which a quantitative analysis of resolution is missing. This paper provides a simulation-based study of the spatial resolution of such methods. We present a criterion of discretion in Non-Line-Of-Sight (NLOS) systems inspired by full width half maximum (FWHM) in traditional optical systems and analyze the horizontal and vertical resolutions of a back-projection-based NLOS system. According to our model, uncertainty in horizontal directions is dominant in NLOS systems. By utilizing this conclusion, we present some potential improvements in spatial resolution by rearranging sampling points, adding a weighting factor, and achieving more than 50% decrease in spatial uncertainty.