NETPAD: An interactive graphics system for network modeling and optimization The practical and theoretical importance of network models and algorithms is clearly documented in the literature. This has resulted in several recent efforts to develop systems for network modeling, algorithms and/or visualization. The main goal of this paper is to describe NETPAD, an interactive graphics system for network modeling and optimization. There were several factors motivating us while developing this system. First, network are inherently visual; so an interactive graphics interface was considered to be a vital component of the overall design. Second, data form a very important part of network modeling; therefore, we have integrated network attributes and tables into the system. Third, algorithmic needs change over time to meet users’ needs for additional functionality or performance, and to meet the needs of specific applications; so we have designed the system to be customizable and expandable. Fourth, widespread use of sophisticated methods requires ease-of-use in addition to functionality; so the system includes a menu-driven user interface, standard file formats and algorithm animation. NETPAD is a portable system written in the C programming language for workstations with the UNIX operating system and the X Window System.