I'm afraid you'll need to do that manually after doing some research

Ask on the Google Maps Local Guides website (requires sign up) maps.google.com/localguides

There exist mapping services that let you manually draw areas to avoid. Would that suit your or their needs, or do you/they need a mapping service that already knows what the "bad" areas are?

The latter @gerrit, but I guess what johnnyjanko mentioned in their answer leaves no hope for such a service.

Note that the word "ghetto" in the US has racist overtones. Historically it related to forcibly segregated Jewish communities in WWII, but in the US it is taken to imply African American communities.

@PeterM The term "ghetto" is from the late Middle Ages, much older than WWII, but yes, it originally referred to areas populated by Jews. In present day it can refer to an area populated by any minority group.

Thanks @PeterM, as a European I thought that because many African US Americans were using that word in their songs, etc., it was acceptable; nevertheless I edited my question to avoid such a misunderstanding.

@gsamaras using words from songs by African American artists while not being an African American yourself is a sure way to get into a lot of trouble in the US.

Although it feels a bit paradoxical @littleadv, I believe you are right; I've updated my post, but if you have any further recommendations let me know, or feel free to edit directly - thanks for the tip!

@Johnnyjanko I believe ghetto is used to refer to areas populated by poor minority groups. A gated community in Luanda where all the rich white Europeans live would not usually be referred to as a ghetto, I think.

For future reference, I have never heard of people in a bad neighborhood reacting poorly to you turning around and going back the way you came.

@AzorAhai-him- It can depend on your body language. If you appear to be slinking away, then that can advertise that you are an easy mark. On the other hand, if your strut purposefully it can make you seem like you belong. Of course if you simply look like a tourist nothing can help you - as I found out both times I was robbed while traveling.

@PeterM exactly. Don't act like a tourist, dress like a tourist, wear funny clothes and hats, and speaking of that, never ever come to San Francisco in shorts. That's for L.A.

If they are getting a rental car, definitely advise them to purchase the extra warranty so if anything happens to the car they are not liable. I've driven in cities all over the US and San Francisco is the only place where someone smashed the window to try and grab something. Only later did I learn that smash and grabs like that are fairly common there. Also, obviously, tell them not to leave anything valuable in the car.

@littleadv that's true, and I would emphasis for others that's "in the US".

Simply turning around seems unlikely to increase your risk, especially as compared to going deeper into a dangerous neighbourhood. Turning around is something people do all the time, and the idea that other people would judge you for it is a common idea, but most people just don't concern themselves that much with what strangers do or why. If anything, it could show a higher degree of awareness of your surroundings, and thus decrease your risk (an "easy mark" is someone who doesn't know or care what's happening around them). Of course, showing signs of being nervous could increase your risk.

I agree about car rental extra warranty. I disagree for turning around, because maybe I was too laconic when explaining the event; I froze because of the scenery I was witnessing, turning around to the direction I came from may be interpreted as running away/avoiding that neighborhood. I have heard from other tourists been (thankfully, only) verbally attacked by the people they turned around from; maybe I overcomplicated the situation and nobody would care if I'd turned around - but in any case prolepsis is key here!

Eyeroll Not everything is racist.

Frankly, and sadly, San Fran is on my do not visit list.