City Parts   Macrae-Gibson Architects focuses on the component parts that make up the principal social organs of the city. These include libraries, schools, hospitals, housing, workplaces and places of entertainment. The firm has completed many projects in these various categories and continually seeks to expand its experience with other related urban components, such as churches, museums and transportation buildings. Dense urban conditions, such as those in New York, can require new buildings, but frequently the architectural challenge is to modify an existing condition. This can involve many levels of intervention including radical transformation and addition.