If you're thinking about moving to Philadelphia, or relocating to a new neighborhood in Philadelphia, you should definitely do some research into the area using the Philadelphia Police Department website or other crime-mapping websites. Not only will this info let you know the crime rate in the neighborhood you are looking at, but it will also tell you what types of crimes normally happen in the area. These things are good to know, especially if crimes like burglary, assault or robbery happen often in the neighborhood.
Philadelphia, in general, has a high crime rate. It's hard to pinpoint definite areas where crimes happen more often, because crime is fairly rampant in the city. However, some of the more notable areas for crime include Rittenhouse Square/Center city (mostly theft), the Newbold area, Cobb Creek, around Temple University and in Fern Rock.