This document discusses using web-based GIS tools for change detection from satellite imagery before and after floods. It provides an introduction to GIS, describing it as a system for capturing, storing, analyzing and displaying spatially referenced data about the Earth. It also describes the key components of a GIS system, including spatial data input and storage in either vector or raster data models, as well as GIS software for transformation, analysis and output. Finally, it defines change detection as highlighting differences in imagery over time to update features based on new information.