The United States Environmental Protection Agency (USEPA) operates and maintains a public access map server (http://www.epa.gov/enviro/enviromapper.html) that hosts a series of Internet interactive mapping applications using Esri's MapObjects Internet Map Server (IMS) technology. These applications provide the public with easy Web access to interactively display and query a variety of geographic and environmental data at national, state, county, and street levels. This article discusses many critical technical issues on how to configure and operate large-scale MapObjects IMS applications on the Internet. The results of extensive tests designed to evaluate the performance of different configurations under three different scenarios are presented. Recommended configurations for supporting successful MapObjects IMS applications are included.