For electronic simulations to be be useful in the design process, all components used in the simulation must have attributes that match those of components in the design, or are similar and provide a realistic basis for analysis. This sense of realism is achieved by correctly mapping SPICE (Simulation Program with Integrated Circuit Emphasis) models to components.
Simulation SPICE models can be added to individual components in a library, or to multiple components in a schematic design by selecting them as a group. If you add SPICE maps to components in your libraries, these components will be ready to use in circuit simulations without mapping. All components in the supplied libraries ngspice-digital and ngspice-simulation have SPICE models, so they are ready to use in simulations. For other components, SPICE models are available from the manufacturer or on the Internet.