12 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. FOSS4G2006 - Free And Open Source Software for Geoinformatics Session 3 : GRASS Desktop James Westervelt james.d.westervelt@erdc.usace.army.mil Michael White michael.j.white@erdc.usace.army.mil James Westervelt james.d.westervelt@erdc.usace.army.mil <MaKaC.conference.ContributionType object at 0xb36f0cec> GRASS