USE WITH CAUTION: The County Assessor’s Maps

By | September 8, 2019

You need to read this post if you use online county government maps.

The Takeaways

  1. What boundaries are is a matter of law; where boundaries are is a matter of fact.” Evidence and Procedures for Boundary Location, sixth edition, page 3.
  2. A court of proper jurisdiction may determine the extent of a property owner’s rights, which is the matter of law.
  3. A surveyor may be needed to determine the physical extent of a property, which is the matter of fact. That surveyor will base their work on the property’s chain of title. That chain of title may require some research.
  4. If you want an accurate map of a parcel, to include any easements and rights of way of record, you should hire a surveyor. A surveyor is the only person who can make you an accurate map of your property. Even then, it will come with a few disclaimers as to what on the map can be considered accurate. For example, if the surveyor overlays a scale drawing of your property boundaries over an aerial photo, the surveyor is unlikely to attest to the accuracy of that aerial image.
  5. If you are involved in a boundary dispute, hire a surveyor and an attorney that practices in this area. But first go read “Ancient Boundary Issues,” another Geodicta post.

Many people who I have encountered as a GIS guy, if not most people, believe that they are looking at property boundary maps when they view the web map portals that some Missouri county assessors are kind enough to provide. Many of these people will see a property line for their parcel that may not look right to them, and then some of them will lose their ever-loving minds in the county courthouse, before the reality of the situation can be explained to them.

I Have Way Too Much Professional History with This Issue

In my nearly two decades of working in local government, I encountered numerous highly-agitated citizens who either raged against their neighbor or my employer, the local government. Often before I could explain how tax maps do not determine property lines and rights, I’d get to sit through a 20-minute lecture on the Constitution, property rights, and why I was furthering a big-government agenda. What was even more confounding was that, once the difference between tax maps and a survey was fully explained, many of these same citizens demanded that the government survey their land and mark their boundaries at its cost. After all, “What do I pay all these taxes for?”

I do not miss those days.

Links to some example Missouri county assessors’ maps:

Why Discuss This Topic, Besides Its Obvious Benefits for Personal Catharsis?

Knowing how property boundaries are mapped versus how tax maps are prepared could help numerous citizens, Realtors®, and others avoid liability from making incorrect and costly assumptions about where and how a property line might be located.

A Reading from Brown’s

In most instances, little or no effort is given to accurately locate individual parcels in relation to each other. Courts have held that the tax maps cannot be used as evidence to ascertain boundaries; they can only be used to identify who is paying taxes on the parcel.

Brown’s Boundary Control and Legal Principals, seventh edition, page 25; bold emphasis added by me, your pal Chris
Cole County’s tax map showing a small portion of the City of Jefferson, Missouri.

If you look at the image above, you’ll notice that parcels are bounded by a polygon, and the streets are not bounded by a polygon. That is because the streets are owned fee simple by the City of Jefferson. Municipal property and several other types of property are exempt from county tax assessment procedures. Typically, only that real property which has the potential to be taxed is drawn on a tax map.

TIP: Read the Web Maps Disclaimer. No Really!

Your Missouri county assessor may be offering you a very smart and handy tool by publishing the county’s tax maps. And if you would only read the disclaimers, I mean REALLY read the disclaimers, you’d understand why you may need to do more research before you go to war with your neighbor over a property boundary dispute.

Here’s an example disclaimer:

Boone County, Missouri, GIS Dataset Disclaimers – Assessor Dataset Disclaimer:
(I’m not picking on Boone County. The staff there are likely very lovely people doing great things for my adopted home county. I’m using Boone County’s disclaimer because it covers all the bases.)

  • These maps were prepared for the inventory of real property based on the utilization of deeds, plans, and/or supportive data.
  • In addition, map files are frequently changed to reflect changes in boundaries, lot lines, and other geographic features resulting from changes in ownership, development, and other causes.
  • The existence, dimension, and location of features, as well as other information, should not be relied upon for any purpose without actual field verification.
  • The County of Boone makes no warranty of any kind concerning the completeness or accuracy of information contained on these maps and assumes no liability or responsibility for the use or reuse of these maps by persons not affiliated with Boone County.
  • Use of these maps by any person not affiliated with Boone County constitutes agreement by the user to assume full liability and responsibility for the verification of the accuracy of information shown on these maps.

(Bold emphasis added by yours truly.)

What the Disclaimers Do Not Say

  • There are known gaps, overlaps, and areas of clouded title in every county in Missouri. Yes, in every single county in Missouri, there are long-standing boundary disputes, and it is not the county assessor’s job to solve boundary conflicts.
  • It is the legal responsibility of both of the parties to the dispute to either solve it between themselves or to bring it to a court of proper jurisdiction and let the judge decide the matter.
  • A county assessor’s maps are just accurate enough to stand up in court for the purpose of determining who owes the taxes on a parcel and where that parcel is generally located.
  • The county assessor is under no obligation to even provide online web maps, let alone provide survey-grade mapping.
  • Some county assessors provide these maps simply as a service to the public. Not a bad move for an elected official. 😉
  • Online web maps greatly aid the local citizens and business community. Online web maps are like rocket fuel for local economic development and good decision-making.
  • The county assessor’s main job is to systematically classify land so that it might be taxed to fund the government.
  • Property boundary disputes are 99% fact-driven. The facts matter, and once they are determined, the existing Missouri case law mandates the proper solution.
  • The original parcel boundaries, per the deed, may be in error and that isn’t the county assessor’s problem.
  • If you want the deed to your property fixed, it is up to you to hire the people with the skills to make the corrections. This may involve a title company, an attorney, and a surveyor working together.
  • County assessors have something called limited sovereign immunity. It means you aren’t going to be able to take them to court and punish them for some great injustice if your tax map boundaries are mapped incorrectly.
  • You may convince the court to order the assessor to correct the error, but you are very unlikely to be awarded compensation for years of overpaid taxes, punitive monetary damages, or attorney’s fees for something that was the fault of the assessor’s office.

Let’s Back This on Up: What Is the Definition of a Boundary?

So, what is a boundary? Black’s Law Dictionary gives this definition: “boundary (1598) 1. A natural or artificial separation that delineates the confines of real property <the creek serves as a boundary between the two properties.> See Metes and Bounds. ‘The object of all rules for the establishment of boundaries is to ascertain the actual location as made at the time. The important and controlling consideration, where there is a conflict as to a boundary, is the parties’ intention whether express or shown by surrounding circumstances…'” 111 C.J.S Boundaries § 3 (1995)

Tax Maps and the Very Nice People Who Make Them

An assessor’s tax maps represent a balance of resources and effort. A tax map only needs to be just good enough to ensure the property that is subject to taxes has its area measured so taxes can be assessed against that property. It would be a complete waste of government resources to expect assessors to keep their tax maps to survey standards. And frankly, it could be an infringement into the proper domain of the professional Missouri surveyor.

While no one really likes to pay taxes, fairly and transparently assessing taxes is what keeps our civilization running. The assessor and the mapping team in the assessor’s office keep the wheels of government running.

And by the way, the people who make your tax maps are often members of the Missouri Mappers Association, and they take great pride in their work. If it weren’t for their cheery, helpful nature, we’d all be worse off. So, when you go talk to the mapper in your county assessor’s office, please be nice.

Two Handy Terms You Need to Know

  • Gap – An area between two or more boundary lines with no clear ownership ascribed to an abutting owner. These are rare.
  • Overlap (gore) – An area where two or more boundary lines cross, with no clear delineation between competing ownership claims by an abutting owner. These are much more common than gaps.

Do you know what the number one objective of the tax mapping and assessment process might be? It is to tax everything that can be taxed under the formula the state hands down to the county. So, there is a clear incentive to make sure there are no gaps in the tax lines. To be fair to everyone who owns property, every bit of taxable property needs to be included on a tax map. One of the most important factors in tax mapping is determining the amount of land, or the total area, to be taxed. This is because the formula for assessing taxes use the area of a property in its equations.

Not surprisingly then, there are many more overlaps than gaps in assessors’ maps. So, while I wrote “two handy terms” in the heading of this section, it might be more accurate to say “one handy term and another you’ll almost never use.”

Missouri’s Tax-Map Preparation Regulations

In 2 CSR 90-65, Missouri’s Cadastral Mapping Standards, the state goes to a bit of trouble to define digital cadastral maps and their role in serving the state government’s need to fund itself and its sub units.

Specifically, SR 90-65 provides three key definitions, and I quote:

(1) Cadastral Data—Source information used to delineate the geographic extent, quantity, and dimensions of cadastral parcels. Source information includes the United States Public Land Survey System (PLSS), subdivision plats, land surveys, real estate conveyances, right-of-way plans, etc.

Map of the Public Land Survey System.

(2) Cadastral Parcel Mapping—The delineated identification of all real property parcels. The cadastral map is based upon the United States Public Land Survey System (PLSS). For cadastral parcel maps the position of the legal framework is derived from the PLSS, existing tax maps, and tax database property descriptions, recorded deeds, recorded surveys, and recorded subdivision plats.

Aliquot parts illustrated.

(12) Tax Map—A document or map for taxation purposes showing the location, quantity, dimensions, and other relevant information pertaining to a parcel of land subject to ad valorem taxes, commonly known as property taxes.

Musings on the Accuracy of Tax Maps

There are many factors that can affect the accuracy of the online parcel map your county assessor provides:

  1. Digital Accuracy: Parcels located within a recently platted subdivision in a sophisticated county—which has a highly trained GIS mapping staff and requires the surveyor to submit survey-grade digital plans for the subdivision prior to its acceptance by the local governing body—are very likely to be, but not guaranteed to be, just as accurate on the digital map portal.
  2. Established County GIS Program: Parcels located in a county that has some form of digital mapping are likely to be more accurate than parcels in a county that still uses hand-drawn tax maps.
  3. City Web Map Portals: Note that no Missouri or Kansas municipalities that I have ever encountered map their own parcels. This is the domain of the counties. So, if you are on a municipal web map portal, those boundaries were likely created by the county and then shared with the municipality through some sort of inter-local government agreement.
  4. The PLSS Digital Framework: If the tax maps are hung on an accurate and updated digital version of the Public Land Survey System (PLSS), their accuracy is enhanced.
  5. The U.S. Surveyor General: Parcels located in a county that had numerous original plats from a well-established General Land Office (GLO) are more likely to be accurate than parcels in a county that had a messy GLO. Messy GLOs are attributable to a number of factors, best explained in this book.
  6. The Hand-Drawn Maps Still Exist: Be wary of parcel accuracy in a county that still produces hand-drawn tax maps. Parcels in a county that recently made the switch from hand-drawn maps to digital maps may also take a few years of massaging before their accuracy rises to the level that a well-established digital mapping program provides.

Additional Links

Link of the Week

It’s a movie! The Lonely Halls Meeting, a GPS documentary – View it on Amazon Prime | View the trailer on YouTube | IMDB page. This movie tells the story of the origins of the Global Positioning System (GPS) in a way that only geography geeks and former bureaucrats can truly appreciate. Many of the scripting, editing, and narrative choices are questionable and somewhat ineffective, but the story and the interviews offer some really cool insights into the story of GPS.

“GPS was created in a small conference room at the Pentagon over Labor Day Weekend in 1973. The decisions they made at that meeting [have] impacted your life in ways they could not have imagined. Without GPS, there would be no internet, no online banking, and no cell phones. Everything from farming to transportation to emergency services has benefited from GPS. But it almost never happened.”, The Lonely Halls Meeting a GPS Documentary, (last visited September 8, 2019

If you enjoy this blog and know someone else who might enjoy it as well, please share the link.

About the Author

You can view Chris Dunn’s third person singular CV here. Basically, he’s a geographer with a law degree, a bar card, and a kick-ass GIS workstation. Email me at