Get It Surveyed

Why Doesn’t My Survey Match GIS?

A common question I get asked as a Professional Land Surveyor is, “Why doesn’t my survey match the GIS records?”

If you’re not familiar with GIS, it is a system used for tracking, mapping and locating property records and information. As surveyors, we use GIS extensively. Honestly, I don’t know how I would do my job without it.

Without GIS, it would feel like going back to the pre internet stone ages, driving down to the County Register of Deeds office to research each parcel and look up old deeds and plats. Don’t get me wrong, occasionally we do have to do this for a parcel, but it would be a nightmare trying to run a modern, efficient business in this day and age. It wasn’t that long ago that our surveying forefathers, the ones whose work we retrace on a daily basis, were doing exactly this for each survey they performed. Man, I have admiration for those guys.

GIS stands for Geographic Information System, although I like to think it stands for “Get It Surveyed,” as one of my college professors used to joke. I won't bore you with the extensive history of GIS, but computerized GIS dates back to the 1960s. Most counties across the country have now adopted a version of GIS that can be accessed by the public.

With mobile apps using GIS information, such as LandGlide, Regrid and numerous hunting and outdoor apps, access to property information has never been more available. You can pull out your phone and see what appears to be a property line almost instantly.

This is where some of the confusion starts, and as a Professional Land Surveyor, it is our job to separate fact from fiction.

County GIS departments do an amazing job of plotting old deeds and maps and piecing them together in a graphical interface. Unfortunately, some of those old deeds and maps contain errors, ambiguities or measurements that do not mathematically close at the level of precision that we use today. Over the years, property descriptions may also have been copied from one deed to the next, sometimes introducing simple transcription errors along the way. A number may have been typed incorrectly, a distance changed or even a bearing mistakenly switched from northeast to northwest. Combine that with changes in road rights of way, subdivisions, recombinations, easements and decades of different surveys being pieced together, and we start to see why we can’t fully rely on GIS to identify property lines.

These plotted property boundaries are then overlaid onto an aerial image, and the two may not line up perfectly. Maybe it looks like your driveway or shed is over a property line when a boundary survey later shows that it is actually feet away. When your neighbors see that and come demanding that you move said driveway or shed, it’s time to get a survey to verify where the property line actually is.

So how do we as land surveyors determine your property boundaries?

I can’t speak for other surveyors, only myself, but the first step in my process is to find the property on the county's GIS website. This gives me information as to who owns the property, the current recorded deed and plat, and other pertinent information such as flood zones and possible easements. I also note if I see anything of concern, like a driveway or shed over a property line.

After I research the property and save the recorded information, I begin to plot the property and the adjoining properties in an AutoCAD program designed specifically for land surveying. Here we can see if there are any mathematical errors, what types of property corners we need to be looking for in the field, and whether there may be boundary overlaps or gaps between properties.

If everything looks good and no more research is needed, then we can head to the field, where the real investigation takes place.

Once onsite, we begin to look for property corners using a metal detector. These property corners can vary from parcel to parcel and sometimes include a piece of rebar, a steel pipe, an old car axle, or possibly a tree or old stone. What we find depends heavily on the age of the property and the general area. It's common to find ½ inch rebar as property corners in newer subdivisions located in urban areas whereas it might be more common to find old axles or stones on larger tracts located in rural areas.

So we’ve managed to locate what we think are the property corners. Now we use our instruments to measure them. You know the camera looking thing on the tripod? Well, it’s not actually a camera. It’s called a total station. A total station allows us to precisely measure angles and distances between the property corners and other evidence we find in the field, such as fences, structures and other improvements. Depending on the property and site conditions, we may also use GPS surveying equipment.

In a perfect world, our job would be done. But finding and measuring a few pieces of rebar doesn’t automatically tell us where the property line is. We then need to analyze that data to determine whether those property corners actually agree with the records we researched and plotted in the office. Do the corners agree with the records? Are the adjoining deeds or plats consistent with the measurements and other evidence?

Sometimes everything fits together like a puzzle. Other times, it doesn’t. We may find that a property corner is missing, the measurements don’t match the records or different pieces of evidence seem to contradict one another. This is where the surveyor has to evaluate all of the available evidence and possibly make multiple trips to the site to determine the boundary.

And that brings us back to the original question: Why doesn’t my survey match GIS?

Because GIS and boundary surveys are two different things created for two different purposes.

GIS is an incredibly useful tool. As I said earlier, I use it on a daily basis and honestly would not want to survey without it. But the property lines shown on a county GIS website or mobile app are a graphical representation of property records and are not a substitute for a boundary survey performed by a Professional Land Surveyor.

A boundary survey, as briefly described above, is an extensive process that combines record research with physical evidence and precise measurements collected in the field. We then have to analyze all of that information to determine how the evidence on the ground relates to the recorded documents. Sometimes the final boundary survey will be very close to what you see on GIS. Other times it won’t.

So if you’re curious about who owns the vacant lot next to you or how much it sold for, GIS is a great place to start. But if you’re planning to build a fence, construct an addition or are buying a property, don’t rely on the line you see on your phone.

Remember what my old college professor used to say: GIS: Get it Surveyed.