The simulation of an electromagnetic transient is only as good as the model's data and the level of detail put into the modeling. One parameter with influence in the results is the size of the modeling of the area around the switched-on line. If the area is too small, the results are inaccurate. If the area is too large, the simulation requires a long period of time and numerical problems are more likely to exist. This paper proposes a method that can be used to estimate the depth of the modeling area using the grid layout, which can be obtained directly from a PSS/E file, or equivalent. The simulation of electromagnetic transients in cable-based networks requires larger computational effort than in an equivalent overhead-line (OHL)-based network. Therefore, the method is demonstrated for the former, with the cases of OHL-based networks and hybrid cable-OHL networks addressed in a future paper. One of the main reasons behind the long simulation times of a cable-based network is the simulation of all the cross-bonded sections. The introduced method can also be used to minimize the modeling of the cross-bonded sections.