A location survey is a professional drawing showing the boundaries of the property you are purchasing. It will be required for closing unless you are purchasing a condominium or other home that does not include property. If there is any question about property lines, however, you may want to order a stake survey (where a surveyor actually comes to the property, measures, and sets stakes around the perimeter) prior to the closing. This is expensive, but it will be worth it to avoid problems later.
If a survey is required, it will be drawn by a licensed engineer and will depict the property boundaries, the location of the residence and any other improvements on the property, and the existence of any easements. (An easement grants someone else the right to use your land. Public utilities may require easements, for example, or your neighbor may have an easement on your property if his/her property would otherwise be inaccessible.)
Use the survey to be certain that you are buying all of the land you think you are buying. Look for shared or encroaching driveways and fences. With new construction, make sure that your home does not violate zoning restrictions such as set-back lines (the distance required between your home and your property boundaries).