A plane has problems. Example

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![schematic](https://i.sstatic.net/R3Pr9.png)

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When you expect certain (hopefully nearby) nodes of the Ground Plane to have ZERO volts between those two nodes, that will not happen. Slits can be your friend, to prevent the interfering currents passing along the path between your two sensitive nodes.

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![schematic](https://i.sstatic.net/GRq0O.png)

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Take a copy of the schematic, printed out, and draw **ALL** the ground currents. Label their values and frequencies and edge-rates. (inductance may matter).

Now start planning how to keep the noise currents away from the GROUND nodes of your sensitive (feedback voltage dividers) circuits.

[oh Magnetic and Electric fields also matter]