It can be difficult to locate activities that generate noise within urban patterns such as highways, airports, 
factories, and other activities.  A new GRASS landscape analysis program r.decay.noise converts a map of 
residential patterns into a map of complaint probability associated with placing a given noise source anywhere 
within a study area.  We will introduce and explain the approach used in this tool and demonstrate its 
applicability.  We will also introduce use of a related tool, r.decay, to generate maps of night sky illumination 
caused by urban patterns.  Both can be useful in the identification of historic and projected changes in land 
use opportunities.