When resources can be ordered based on a property or on some externally-defined numbering system, that order can define draw priority. For example, trucks of varying size can be sorted by their loading capacity, where it may have been decided that larger ones will be loaded first; an engineer may have numbered footings to specify the order in which concrete is to be placed, where those with lower numbers will be placed first. Selection is thus based on comparing an individual resource's "capacity" or "placement number" property with that of others in the same queue. Other examples are "easiest to install first" and "highest ratio of ear nedto-expended effort first" (Howell and Ballard 1996),
"materials covered by or buried in others first," and "those that can easily be damaged last.