What makes a safe Neighborhood?

Say I walk through a residential neighborhood and see a four boarded up houses in four blocks but I also see several churches, an elementary school and late model cars-ford, mazda, not Mercedes or Jaguar but not rusted 20 year old chevy's either. I don't feel threatened walking there at 11:00 pm, I hardly see anyone and when I do it some folks sitting on the front steps talking or someone walking/talking on a cell phone.

But later my friends tell me they wouldn't live in that area. What's this about?
What should I be looking for as signs of a "safe" area?

I've looked at crime rate maps, which would seem to be the most objective way of knowing but they are not detailed enough. They lump huge areas toegether.

In New York more and more neighborhoods are safe. You should generally avoid areas that are known to be unsafe. In Manhattan, it's areas above 110th St, Washington Heights, etc. In Queens the bad areas are Jamaica, etc. In Brooklyn, you should avoid Crown Heights, Bedford Styvesant, East New York, etc. Basically, avoid poor, undeveloped areas where there are crappy stores, poor businesses, graffity on the walls, small, drity-looking supermarkets, poor-looking cafes and services. Also, I would avoid areas that are empty at night. Even if it's objectively considered safe, you don't want to walk empty streets every night. "Unsafe" people can venture into a "safe" areas and meet you there when no one else is watching. Again, more and more areas in the city are safe. It's been told many times but I can repeat that New York City is the safest city in America. Usually, good/lively neighborhoods that are suitable for comfortable live and have many restaurants, good grocery stores, clean streets and nice-looking buildings are also safe. Another way to judge is to look at real-estate prices. If you have to pay over $1200/month for one-bedroom, it's probably a safe area.

Although I live in Brooklyn and pay $950/month for 1-bedroom and my area is pretty safe.

Good answer to a hard to explain question Leo.