The development of a general purpose disaster impact assessment software package is a daunting task, complicated by a number of technical, political, and administrative challenges. For example, geospatial information management should account for the administrative system of the country subject to the assessment, while the hazard, fragility, and inventory each have features that require implementation and display decisions that are consistent with the region. To accommodate the requirement of Istanbul, as possibly the largest megacity in the world with an acute earthquake risk problem, a new software package was developed, based on the Mid-America Earthquake Center platform MAEviz. MAEviz-Istanbul, the first stage of HAZTURK, is described in this article with emphasis on the regional significance and consistency of the development from an earthquake engineering viewpoint. Sample analyses are also provided at the end of the article to demonstrate the potential use of such a tool in assessing the impact of earthquakes on a densely populated cosmopolitan region.