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Hi, If I connect 2 metals with a via that has the minimum dimensions allowed according to DRC rules, is there any kind of problem? I'm curious to know why when I render the layout, the via "shrinks", what happens there? Thanks in advance

Magic's drawn vias are a derived layer that is approximately the same as a LEF "via rule".  It represents an area that contains one or more contact cuts plus overlapping metal.  The 3D view shows you the GDS layers, so you see the actual contact cuts.  You get the same result by doing, e.g., `cif see VIA1` (which is a "feedback" drawing that can be cleared with `feedback clear`).

FYI, the DRC rules in magic will tell you things like the minimum size you need for the contact area, which is different from the (exact) size of the contact cut.  You can draw the contact layer any size you want as long as it fits at least one contact cut with sufficient metal overlap.