We use three dimensional particle simulations to explain how latent images of lines form in xerographic development systems. Our computational model uses the particle-in-cell technique to track toner particles in time and space under the influence of the numerous forces of xerographic development. Using physically realistic models of toner adhesion, cohesion, air drag, and friction; detailed particle trajectories can be calculated and monitored in selfconsistent electric fields. Examples of thin isolated lines, both parallel and perpendicular to the process direction, are analyzed for variations in mass and charge density. Details of the development process are shown to affect the image quality of individual and grouped lines (i.e., ladder charts). Excellent agreement has been observed between simulated development subsystems and experimental data.