It is also worth noting that the graphs of lethal ranges of weapon effects as a function of yield, that are commonly encountered, are the unobstructed "open air", or "free air" ranges that assume among other things, a perfectly level target area, no passive shielding such as attenuating effects from urban terrain masking, e.g. skyscraper shadowing, and so on. Therefore, they are thus considered to present an overestimate of the lethal ranges that would be encountered in an urban setting in the real world, with this being most evident following a ground burst with explosive yield similar to first generation nuclear weapons.