The problem is that the right answer is a complex Boolean function.
Depending on the local laws, some or all of these elements may impact your ability to open carry:
Permit Required (Y/N)
State Pre-emption (Y/N)
Shall Issue (Y/N)
Element of Crime or Affirmative Defense?
The last one is particularly tricky. If having a permit is an affirmative defense, then you are presumed to be a criminal simply by the act of carrying. Showing a permit SHOULD end the encounter, but some LEO agencies will use the fact they get an automatic Tier II encounter to maximize the harassment factor. MARTA (Metro Atlanta Rapid Transit Authority) used this loophole for a while to arrest open carriers, search them completely, seize their property, and generally make it impossible to exercise the right on a daily basis. Even when the carrier showed a GWCL, they were detained for an average of an hour or so before they were allowed to go on their way while officers "verified" every single piece of ID they carried. Eventually the legislature had to change the definition of the "crime" so the arresting officer/agency had to have RAS that the person had no GWCL. Even then the legislature had to explicitly list public transportation as not being under the "government buildings" restriction before MARTA got the clue.