Smallest unit of the geographical domain covered by a numerical model, such as a climate or a hydrological model. Because of the complexity of the processes they represent and the limitations of computing power, these models divide up their modelling domain into a juxtaposition of “boxes” called grid cells. In the case of a climate model, the grid cells are tridimensional and are aligned along each spatial dimension. A climate model calculates the state of the climate system in each cell. Currently ISIMIP uses a grid size of 0.5 degrees or approximately 55 km at the equator.