Automated Driving Systems (ADS) require extensive evaluation to assure acceptable levels of safety before they can operate in real-world traffic. Although many tools are available to perform such tests in simulation, the lack of a language to formally capture test scenarios that cover the complexity of road traffic situations hinders the reproducibility of tests and impairs the exchangeability between tools. We propose GeoScenario as a Domain-Specific Language (DSL) for scenario representation to substantiate test cases in simulation. By adopting GeoScenario in the simulation infrastructure of a self-driving car project, we use the language in practice to test an autonomy stack in simulation. The language was built on top of the well-known Open Street Map standard, and designed to be simple and extensible.