The shape and dimensions of nanometer-scale structures were successfully determined using a model-based library scanning electron microscope (SEM) measuring technique. The SEM images were acquired on 10 nm dense integrated circuit lines with a recently developed image composition method, in which blur from drift and vibration were minimized. A Monte Carlo SEM simulator (JMONSEL) produced a model-based library that was interpolated to produce the best match to measured SEM images. The shape cross-section determined by this method was compared to the results of transmission electron microscope and critical dimension small angle x-ray scattering measurements with good, few atoms worth of agreement. The associated repeatability of the average of the SEM results across an image is at the tenths of a nanometer, similar to the results of scatterometry and other area-averaging techniques. Additionally the SEM's native high spatial resolution also permitted revealing defects and other local departures from the average.