Gerber trans of multiple ckts on one board in ADS Layout

Dear all,
If I finish simulating some separate layout circuits and now want to fabricate these layout circuits on one board, I think I should put these circuits together in ADS layout and then export Gerber files. However, what kind of settings do I need to do in ADS layout for me to ask PCB house to cut and separate these layout circuit blocks? For example, in Protel, we usually use keepout layer to set boundaries and cut/separate these subcircuits.
Another question:
When I do settings in Export Gerber Options, what's the meaning of 'Positive' and 'Negative' polarity for different layers?
Do I need to set 'Negative' polarity for ground layer, and 'Positive' polarity for signal layers and via layers?
Thanks a lot.

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