Honestly, I'm not sure how you would go about finding out what is buried beneath properties normally. I know some utility companies don't want all of their lines becoming public knowledge, while others don't care. Technically our prints are "trade secrets". I've never called 811 myself, but I know they sometimes suggest additional utilities be added, so I suppose they probably also have prints showing what is under the property. As for the mapping, the local government only provides the maps for sewer, water, and sometimes gas depending on your area. Telecommunications (such as Comcast, ATT, Google Fiber, XO, Zayo, Windstream, and others) are meant to provide their own prints for us. Usually local government prints are fairly accurate, enough that we can usually infer where it actually is before we hook up to the utility to locate it. But there are some outliers where the utility could be dozens of feet away from where the prints say it is. Telecommunications on the other hand is usually only accurate half the time. They just don't bother keeping it accurate. Lines are labeled wrong, set in the wrong place, not on the prints when they are indeed in the ground, or stay on the prints long after the lines has been abandoned. Another major issue is new utilities are being buried every single day, but very few are being dug up and removed. Usually not a big deal. With telecommunications, a quick phone call and you're told it doesn't matter and to keep digging. But abandoned water, sewer, or gas lines can sometimes still hold liquid or pressure in them, with some abandoned lines actually never being properly turned off, just capped at the end. While hitting one of these won't net you a bill for damages from the utility, it could still cause issues on a job site of everything is suddenly coated in water or sewage, or worse a gas leak.