The advantages of code reuse can not be overemphasized for any corporation as a measure of cutting down application development time and hence the custom application development cost. With the advent of ArcInfo 8.0, object oriented philosophies can be used for GIS application development. This paper discusses how to design and develop a custom ArcInfo 8.0 application using visual modeling tools and COM architecture. The Maine DEP utilized Visual Basic 6.0 and Visual C++ for the majority of the customization and object development. Salient points discussed include necessary considerations for developing reusable code, data persistence, platform selection and security issues. These issues will be discussed within the framework of the Maine DEP enterprisewide GIS application.