Transient to prevent JSON serialization. A possible empty string identifying a context object. Cell size of the internal storage of DynamicElements. Is used in the LinkedCellsGrid. Obstacles of scenario by id. Tree maps ensures same update order during iteration between frames. Sources of scenario by id. Tree maps ensures same update order during iteration between frames. Targets of scenario by id. Tree maps ensures same update order during iteration between frames. TargetChangers of scenario AbsorbingAreas of scenario by id. Tree maps ensures same update order during iteration between frames. MeasurementAreas. AerosolClouds. Droplets. List of obstacles used as a boundary for the whole topography. Used to get attributes of all scenario elements. Used to store links to all attributes that are not part of scenario elements. set dynamicElementIds to values bigger than the biggest initial element to ensure unique ids.