# topo

The pointer to the topography file is a foreign key referencing [name](https://swatplus.gitbook.io/io-docs/introduction-1/hydrology/topography.hyd/name) in [**topography.hyd**](https://swatplus.gitbook.io/io-docs/introduction-1/hydrology/topography.hyd).

The topography variables for Routing Units are used to compute time of concentration for sub-daily routing.