Option 2 seems to bee invalid, as one business (even non-existent one) could obstruct unrelated businesses in a malpractice.

@Basilevs: Google already allows people to log in and "claim" their business so they can curate the Google maps business record. There is nothing inherently "invalid" about option 2, and it does not introduce any more risk than already exists in Google maps. To my knowledge, there is an approval process before you can "claim" your business record, but that won't prevent clever fraudsters from screwing with things. That's also why you shouldn't rely on these mapping services for legally verified information.

Existing APIs (can) use street address as a destination. If a business is allowed to restrict an access to the address, they could direct the traffic to themselves instead of a competitor on the same address.

I also read once (I've since forgotten the source) that Google maps was struggling with law firms adding invalid locations. The law firms were real, but didn't actually have a physical office located at the address they indicated on their business record. The intent was not fraud, but to appear in local search results when people searched Google maps for law firms. Consumers and app developers incur some risk using these mapping services, and there doesn't appear to be a good workaround (hence the OP's question).

And "indicate the business is in a restricted area" is completely different than "block access."

See my second comment - the business may indicate the ADDRESS is in the restricted area and manipulate navigation hints to have unfair advantage.

I think you might be getting stuck in the weeds here. You bring up valid points, but they are no more troublesome than what Google maps already provides.

What's to stop a clever person from claiming a business and then trash-talking people who leave reviews, or uploading incorrect photos? Or entering incorrect hours of operation? Maybe they state the business is closed on Saturdays (typically the busiest day of the week hypothetically) so people go next door to a business that is open? And the person perpetrating this fraud doesn't own the location; they own the business next door.

True, Google maps have all these functions. But we are designing a new map application here (for the question to be on-topic). I guess the solution is to only allow businesses to modify routes where the destination is a specific business.

But malicious business can still direct people to the government territory, so the original question is unanswered.

My solution was to just throw an internal data entry team at it. Never even thought about crowd sourcing the boundaries of area 51.

Would need some curating to make crowd sourcing work.

@candied_orange Oh, that reminds me. I've moved countries and lost the ability to post corrections to Google Maps. They have different approaches depending on the area!

Huh, never experienced that

One concern, if you crowd source these boundaries are you protected from liability? Posts that violate copyright are a bit different than those that could starve a brick and mortar store or run people into a ditch.

@candied_orange My corrections were only applied after weeks of moderation. So that could be a hint of liability.