The police application is a complete waste of time unless you plan to make it a burdensome R/T (real time) map. Since "word on the street" gets around fast, in no time you will have unwanted heat from your local police. First time it obstructs an investigation, bust or sting operation regardless if the police have the tools or legal jurisdiction to tackle you....you will have serious enemies in government. You are making yourself what would be deemed a "security threat". I would advise against it. Before you defend it, EVEN if you used it only for reporting speed traps...sooner or later people would start "reporting" "speed traps" that couldn't possibly exist. The government is going to be less than sympathetic to your TOS violations than you think. Even CL gave up fighting the government cause it just wasn't worth the time, $$$ and effort.
Overall tho your idea is sound. Prostitution isn't going away ever. Legal, Illegal....doesn't matter. People want sex on demand. I had once concieved a website for the advertisment of "escorts" where a reasonable percentage of the gross proceeds would go specifically to trustworthy street level organizations (direct donations) who work to stop pimps, human traffickers & get young girls off the streets. But America is a place where prostitution is Highly Illegal but minimally penalized in most jurisdictions...unless you are marketing it in which case you might as well be running a bordello yourself and face maximum penalties. No matter what the "intent", an operation like the one I conceived is barred from being a 501(c) and any "for profit" operation (regardless of profit or loss) will draw public disqust, law enforcement scrutiny and possibly hefty criminal charges.
Personally, I still believe you can fight evil with evil & that thousands of independent providers are likely to give patronage to a service that dared to cross unspoken lines and actually attempt to keep young girls from having to experience what they likely did. Yes it's exploiting the exploited...but for a good purpose as opposed to creating a "monger" map which any clever pimp could easily manipulate for enhanced profits. The only thing I ever want from a pimp is disclosure. Disclosure in where he keeps $10s of thousands of dollars walled up at. And for that volume of untraceable cash, I'm not picky on the methods used to gain total compliance from him. That's the true irony in America! I am less likely to go to jail & more likely to get money by waterboarding, removing fingernails, spraying with acid, removing digits with boltcutters upto and including disection and drawing and quartering a fellow human being than if I opened a simple website that could lead to his arrest and provide profits for me. America can be really stupid sometimes with it's over abundance of liberalism.