EXPANSE is a spatially-explicit, bottom-up, technology-rich, single-year optimization model of the electricity system. It has a Swiss and a European version. The model accounts for up to hourly operation and long-term capacity investment of electricity generation, storage, and transmission. EXPANSE has three key features. First, the model is spatially resolved that allows for sub-national modeling of the European electricity system (up to NUTS 3 level) or at the level of 2172 Swiss municipalities. Second, EXPANSE applies Modeling to Generate Alternatives (MGA) to compute many alternative scenarios of different spatial configurations of the electricity system with cost-optimal and near-optimal costs. The principle of MGA is to relax the cost-optimal spatial configuration with an acceptable relative cost increase called slack to search for many alternative spatial configuration scenarios. These near-optimal scenarios can have other unmodeled advantages in terms of environmental impacts or feasibility for real-world implementation. Third, EXPANSE quantifies regional impacts associated to the capacity and operation of electricity system infrastructure, including investment and divestment, job gains and losses, and regional impacts on electricity prices, greenhouse gas emissions, particulate matter emissions, and land use.