A frequent question from a user of
"Why is the distance (spacing) between the electrodes is twice less than real in the data file for the 2D inversion program Res2dinv?"

The distance between electrodes depends on the horizontal and vertical dimensions of the cells in the 2D inversion model. Res2dinv's developer, Dr. M.H. Loke, recommends to refine the model:
There are two possible ways to reduce the width of the model cells. The first method is implemented in the Res2dinv itself by using the "Use model refinement" option at the "Inversion" menu. The second method is to modify the data file directly using a text editor. The unit electrode spacing is given in the second line of the apparent resistivity data file.
This method is also implemented in the x2ipi. Here user can refine model here in the "Options" menu: