GiD lets you import geometrical models, meshes or results in the following formats.
Files Menu>Import>Preprocessing
The file browser could allow some extra "Import options", depending on each case.
Usually these options are hidden, press the arrow icon, if any, to show them
e.g.
Most preprocess importations have as extra options the ones related to collapse the model just after be imported:
Automatic collapse after import: To do or not this collapse
Use automatic collapse tolerance: to let the program to get an automatic value of the tolerance, just to join points close that this value.
Tolerance: the user value, in case of not to use the automatic one.
Collapse ignoring layers: the default way: close entities are joined without take into account if they belong to different layers.