We have investigated the nodular defect using computer simulations and experimental techniques. A modified version of the hard-disk model, in which the migration and attraction of atoms are introduced in simplified ways, is used to simulate the formation and development of nodules. This simulation reveals the self-extending nature of nodule growth and the dependence of the nodule shape and size upon the conditions of the coating's formation, including deposition geometry, migration, and capture length of atoms. By planting artificial seeds on substrate surfaces and overcoating with single and multilayer stacks, we have encourged nodular formation under controlled and variable deposition conditions. Fractured cross-sections of these coatings have been examined by scanning microscopy (SEM). A comparison between our experimental observations and the modeling results help explain the mechanisms for nodule growth.