This document discusses principles of Engineering GIS, which integrates CAD and GIS data and tools. It outlines five principles: 1) data passes through a lifecycle from design to construction, 2) data is accessed natively in CAD/GIS tools without import/export, 3) tools enable data creation and maintenance in design and GIS, 4) geospatial analysis and mapping tools are used, and 5) design data is accurately rendered. Case studies demonstrate how the approach improves efficiency across tools, workflows, and locations.