Why Isn't GIS Accurate for Property Boundaries?
🦅Perspective
by Hawkins Geospatial
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No. 006
One of the most common phrases surveyors hear is:
"Well the GIS says..."
And why do we dread those words? The short answer is simple: GIS maps are not intended to locate property boundaries and should never be relied upon to determine ownership or the location of a property line.
In fact, most county GIS websites require users to acknowledge a disclaimer stating that the information displayed is approximate, provided for reference purposes only, and should not be used for legal, engineering, or surveying purposes. Despite these warnings, many property owners mistakenly assume the parcel lines shown on GIS maps represent the exact location of their property boundaries.
What Is GIS?
GIS stands for Geographic Information System. Counties, municipalities, utility providers, and other organizations use GIS to display and manage geographic information such as:
Parcel boundaries
Property ownership information
Tax records
Zoning information
Aerial photography
Flood maps
Addresses and road networks
GIS Is a Valuable Tool—When Used Properly
To be clear, GIS is not the problem. In fact, it is one of the most useful tools available for researching and understanding property information.
In many cases, GIS serves as an excellent starting point when researching a property.
The problem occurs when GIS parcel lines are treated as surveyed property boundaries.
A GIS map is designed to provide a general representation of property information. It is not intended to establish property lines, locate corners, resolve boundary disputes, or determine ownership. Think of GIS as a reference tool rather than a boundary determination tool. It can point you in the right direction, but it should never be considered a substitute for a professional land survey.
The Disclaimer Most People Never Read
If you've ever visited a county GIS website, you've likely encountered a disclaimer before accessing the map.
Most counties require users to acknowledge that:
The information is provided for reference purposes only.
Parcel boundaries are approximate.
The data is not guaranteed to be accurate.
The maps should not be used for legal determinations.
The information is not a substitute for a survey performed by a licensed professional.
Many users click "Accept" without giving it much thought. However, that disclaimer is important because it clearly states the limitations of the information being displayed.
The county is essentially telling users that the map is a useful reference tool, but it should not be relied upon to determine the location of a property boundary.
Why Are GIS Property Lines Inaccurate?
There are several reasons GIS parcel lines may not match actual property boundaries.
GIS Lines Are Often Created from Multiple Sources
Many parcel maps are developed using recorded deeds, plats, tax maps, aerial photography, and other public records. Some of these records may be decades old and may contain inconsistencies or limitations. When data from different sources is combined into a GIS system, small discrepancies can occur.
Aerial Photography and Parcel Lines Don't Always Align
Many people assume that if a parcel line appears to follow a fence, driveway, or tree line on an aerial photo, it must be accurate.
In reality, parcel lines are often overlaid onto aerial imagery and may be shifted several feet, or sometimes much more, from their true location.
Even small errors can become significant when determining where a fence, building, or improvement should be placed.
GIS Is Designed for Reference, Not Boundary Determination
GIS systems are built to display information efficiently across entire counties and municipalities. They are not designed to provide the level of precision required for legal boundary determinations.
These limitations are generally acceptable for planning and reference purposes but are not acceptable when determining property ownership.
Property Boundaries Are Legal Determinations
A property boundary is not simply a line drawn on a map.
Determining a boundary may require:
Researching deeds and plats
Reviewing historical records
Evaluating adjoining properties
Locating existing monuments
Performing precise field measurements
Applying principles of boundary law
This process requires professional judgment and can only be performed by a licensed Professional Land Surveyor.
How Far Off Can GIS Be?
There is no universal answer.
Some GIS parcel lines may appear very close to the actual boundary. Others may be off by several feet, several yards, or even more depending on the quality of the source data and the history of the property.
Because there is no guaranteed level of accuracy, GIS maps should never be used to:
Build a fence
Construct a building
Locate property corners
Resolve a boundary dispute
Determine ownership
Establish setback compliance
The cost of relying on inaccurate information can far exceed the cost of obtaining a professional survey.
When Do You Need a Survey?
A professional land survey should be considered when:
Purchasing property
Building a home
Installing a fence
Resolving a boundary dispute
Subdividing land
Combining lots
Creating easements
Developing property
Locating property corners
A survey provides a professional opinion of boundary location based on record research, field evidence, measurements, and applicable laws and standards.
The Bottom Line
GIS maps are valuable tools, but they are not surveys.
They provide useful information that can help property owners better understand their land, research neighboring parcels, and identify potential issues before a project begins. However, GIS parcel lines should never be treated as actual property boundaries.
When questions of ownership, construction, improvements, or legal boundaries are involved, a survey performed by a licensed Professional Land Surveyor remains the appropriate and reliable source of information.
At Hawkins Geospatial, we help property owners throughout North Carolina understand their boundaries with confidence. If you need a boundary survey, property corner location, subdivision, lot recombination, or other surveying services, contact us today to request a quote!
Have a Question?
Every property and every project is unique. If you have questions about your land or need professional surveying services, we're here to help.
📞 704-750-9246
Perspective is a recurring series from Hawkins Geospatial, sharing practical insights, real-world projects, and professional guidance to help property owners, builders, and land professionals make informed decisions.
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