Advice for GIS techs making maps for the courtroom

By | November 12, 2021

Note: This post is being made with speech to text. So please forgive my errors. I had a little medical event back in August 2021. I am not yet able to fully use a keyboard.

This post was originally a PowerPoint delivered to the MGISAC in a 15 min. presentation. I’ve adapted it for the web. I wanted lay out a few general principles that a GIS tech ought to keep in mind if they’re preparing a map for use in court. I also wanted to touch on how to testify to the origins of the data and the process under which the map was created. MGISAC members can always give me a call if they have any questions. Because a long time ago I promised to use my law degree for good and not evil, thus Missouri GIS techs get free advice. But you know what free advice is worth, right?

Also down at the bottom of the page is a link to a podcast I did with Directions Magazine. It covers much of the same material. Feel free to email me any comments you might have.

-Chris Dunn


  1. Someday your County Attorney, Sheriff, or Police Chief will say, “I need a map for use in court.
  2. Let’s review the issues related to making and testifying about your GIS products for use in a court of law (demonstratives).

This PowerPoint is Not Legal Advice:

  • In accordance with the Missouri Bar Association, the American Bar Association, and the American Dodgeball Association of America, this PowerPoint is not offered as legal advice, nor should it be viewed as legal advice.
  • ALWAYS consult your own organization’s attorney before relying on any of the materials here.

Example Demonstrative

Sixth Amendment

  1. The Sixth Amendment provides that a person accused of a crime has the right to confront a witness against him or her in a criminal action.
  2. This includes the right to be present at the trial (which is guaranteed by the Federal Rules of Criminal Procedure Rule 43).
  3. As well as the right to cross-examine the prosecution’s witnesses.
  4. Also applies to civil cases – in most cases.

Not Your Attorney

  1. The city, county, or whatever organization you work for has their attorney. That person is not your attorney.
  2. Your interests may be aligned but there have been situations where GIS techs were thrown under the bus because that was the easiest way of resolving a case.
  3. If you ever do find yourself in a position where your organization’s attorney is asking you to lie or bend the truth the first thing you do is stop talking. Next, hire your own attorney IMMEDIATELY!

Truthiness? Yes!

  1. Always tell the truth.
  2. Don’t elaborate.
  3. Give concise answers.
  4. Explain it like you are telling you octogenarian grandparent at Thanksgiving what GIS is and what you do for a living.
  5. Your obligation is to the truth, not your team. Hopefully they align.
  6. Always tell the truth.
  7. Always tell the truth.
  8. Always tell the truth.

Be Prepared!

  1. Be prepared to talk about the origins of every data set in your GIS.
  2. Be prepared to talk about why you symbolized items the way you did, the projection you used, the way you store the data, etc…
  3. Know the product you have produced backwards and forwards before you ever get on the stand.
  4. be prepared for some people who are cross-examining you to pretend your map is a pile of poo. They do this to sow doubt in the quality of the product you have produced. It’s a technique that is sometimes effective and at the same time is very disingenuous and in my opinion unethical for an opposing attorney to use.

Your Role

  • The legal team may ask you in detail about any GIS evidence or exhibits that they plan on presenting in court.
  • Let them know right up front if your GIS is based on any questionable or problematic data or processes.
  • Be aware of the best practices in the GIS field for the kind of map you are producing.
  • It should never be a session where the legal team tells you the “right” answer.
  • However, the legal team is allowed to present its theory of the case and ask you questions to see if your GIS products and procedures align with their theory of the case. This is not unethical. This is typically the process where a non-geospatially aware attorney is learning from you and trying to discover if they have any holes in their theory of the case
  • Shocker: Most attorneys are extremely ethical and will not put you in a bad position.


  1. A deposition is a more confrontational style of interview that is taken under oath.
  2. Most technical witnesses do not receive hard grilling’s.
  3. Often, if they depose a technical witness like yourself, it’s merely to get on the record some fact that will support an assertion they make later in court.
  4. Technical witnesses don’t tend to get beat up in depositions or on the stand.

Witness Prep

  1. If your organization asks you to go to court, or you are subpoenaed by the other side, your organization’s attorney will probably do something with you called witness prep.
  2. Or, you may be asked to create a written affidavit of facts.
  3. These are normal and not threatening procedures.
  4. But once again don’t lie, don’t even shade the truth.


  1. Unless you are a licensed surveyor, you don’t have any opinions about the location of property lines
  2. Make eye contact with the jury and the judge
  3. Ask if you can get out of the witness box and point at the map
  4. Rehearse saying complicated things in simple language
  5. 24 x 36” foam core is ideal for most courtroom settings
  6. Understand that one third of humanity is spatially blind (just my guess, not backed up by peer reviewed studies)
  7. You may want to add one layer at a time on separate exhibits to bootstrap the jury or the judge up to a more complex exhibit
  8. Suggest that your attorney use a local map to screen potential jurors
  9. After the court case has been decided get a copy of your testimony for your personal records
  10. Understand that the opposing counsel may be provided with not just a copy of the graphics you produce but your GIS native files. That’s called discovery. If you have any questions about discovery, watch My Cousin Vinny.

Sept. 29, 2021 – Directions Magazine: Podcast: Geospatial Experts as Witnesses

Welcome to another edition of the DirectionsMag/URISA Podcast Series! In this edition, we had a chat with Chris Dunn, Esq. of GeoVelo about his experiences as a geospatial expert witness. Matt Gerike of the URISA professional education committee hosts this episode.

When this post was completed and published the author shows up as Emily Wright. Chris Dunn is responsible for the text of this post. But my new and very able assistant Emily Wright put the webpage together. Thank you Emily.

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