With all the readily available aerial and satellite imagery, it is a legitimate questions to ask if GIS can be used to replace surveyors to understand property issues and to resolve legal disputes involving parcel lines. The ability to access Google Maps or a local agency’s online mapping application to look up parcel lines and overlay them with aerial photography provides a good overview and can provide some answers to property questions. However, all of this geographic data can’t replace legal boundary data.
Property lines are not physical entities that are visible on aerial imagery or on base map data such as street networks. Those lines are created through a network of reference points (usually markers or “monuments” buried underground) and surface measurements between those points. This is what surveyors call “ground evidence,” or legal boundary data.
GIS data is pulled together from a variety of sources with varying degrees of accuracy and precision. Overlaid together, the error found within each dataset is amplified. Therefore, overlaying a parcel database that may have an accuracy of +/- 10 feet onto aerial imagery with an accuracy of +/- 30 feet can lead to features ending up over 80 feet away from their true point. In addition, sometimes the source data is unknown, and the accompanying metadata is missing that would provide the user with an understanding of the currency and accuracy of the data.
Legal disputes that arise over the precise location of property boundary lines need to be resolved based on the origination and use of legal boundary data documented over time by licensed surveyors. Surveying is highly regulated and comes with legal requirements for the methods used to record property information. Surveyors are required by law to meet standards for experience and to pass examinations in order to be licensed. These laws are, in effect, consumer protection laws that ensure property rights and public safety. Therefore, locating your property lines on the ground will still require the preparation of a current survey from a reputable, professional land surveyor.
If you want to avoid potential conflicts with your adjacent property owners that might lead to litigation, a proper land survey provided under the duties and obligations of professional licensure is still your best insurance. If you are ever sued for encroachment of another’s property, which can be a financial burden for most individuals or businesses, a professionally prepared and sealed land survey, based on the highly relevant legal boundary data, is still an excellent defense.