1 [ESRI software] A layer that references a set of CAD data. CAD data is vector data of a mixed feature type. CAD layers may be of two types: CAD drawing dataset layers, in which one map layer represents the entire CAD file, and CAD feature layers, in which data is organized by geometry type.
2 [non-ESRI software] A component of a CAD drawing file. CAD layers are the digital equivalent of acetates in overlay drafting, and are powerful tools for organizing a drawing into logical categories. CAD layers and levels may be managed with ArcGIS. In MicroStation, layers are also referred to as levels.