PLSS Remonumentation Alignment

Question

I am looking to see if anyone in this group has gone through the process of PLSS corner remonumentation in their area and adjusted the parcel fabric data to match the more accurate corners. Our county has quite a few corners that have been GPS'ed, and I would like to start the process of adjusting our fabric data to the new corners. I have done some research online, but I would like to get some tips/best practices from someone that has done it before. Thanks in advance!

MikeZummo · Answer

Hi Adam,

I am glad to help out with any questions you have. I sent you my contact info via direct message.

Mike

AdamHart1 · Answer

@MikeZummo @AmirBar-Maor

Thank you both for your input on this. A little more background on our data...It is just in a FDGB since I'm the only one editing it right now. The base PLSS framework that was used to to develop the current data was from the 1990s, and the base parcel data was initially developed around 2006-2007. I've been working on it for the last 10 years or so by implementing the ArcMap fabric and then upgrading to Pro about 3-4 years ago. I have started going through topology errors and finding the tiny lines and fixing them. This will be quite a process. At the same time, co workers have started going in the field to collect Remon corners with our GPS that we don't have GPS coordinates on yet from the surveyors. Then once we get enough corners GPSed, I will start the adjustment process. So @MikeZummo would it be possible to get your contact info for any questions I may have? If not, that's okay. Thanks!

MikeZummo · Answer

I agree with everything Amir said, make sure the data is clean before the adjustment. Topology issues can be exacerbated by an adjustment. Definitely run the consistency check, it will find data entry blunders. Here is the best advice I can give when adjusting the PLSS:

* A priori error estimates on the lines are pretty key. Direction and distance accuracies have to be realistic for the surveys. If you are adjusting using survey measurements from the 1860’s, chances are good the 30” and 15 cm defaults will not be loose enough to adjust the measurements between GPS points. If you have new survey measurements, make sure they are held tighter than the stuff from the 19th century - you want to avoid having older and likely poorer quality measurements degrade the accuracy of the new measurements. Don’t let the tail wag the dog.  
* Azimuth Types – If you are using GLO/BLM measurements, remember they report bearings at the midpoint of the line (mean geodetic). You can use the Azimuth types in the adjustments if you are using 3.2. If you aren’t in 3.2 yet, you may need to loosen the direction accuracies to accommodate the rotation between ground and grid.
* Sometimes it may be a good idea to constrain the adjustment area by setting points on the edges as fixed and constrained temporarily, especially if the movement would be insignificant on those margins and there are other datasets lined up to them already.  It's not fun having to re-align vertices in associated feature classes by a few centimeters because of an adjustment. If the movement is that small, how much improvement have you really gained on a line a mile long? You can also exclude movement less than a certain tolerance when you apply the LSA.
* Control – sounds like you have good GPS measurements to use, but you should still assign realistic XYAccuracies to them. For example, you wouldn’t want to hold a resource grade GPS point like it was survey grade. If you have all 8 monumented points on a section boundary, you may be able to just conflate and re-subdivide.  Remember, unless the plats say otherwise, 16th corners are usually at midpoint between section and quarters. If you do not include them in the adjustment, you should re-midpoint them afterwards.
* Re-subdivide after the adjustment – the positions of the aliquots and lots in the interior of a section are determined by the positions of the points on the section boundaries. You can’t just divide a section up into 16 equal area parts and call it good. The record may say 40 acres, but the survey measurements can stretch and shrink those subdivisions. Refer to chapter 3.99 of Manual of Surveying Instructions 2009 (blm.gov) to see how these should get drafted.
* LSA's are an iterative process, you will end up tweaking things as you go. I find selecting the lines works best for me, but as I am working through adjustments, I end up unselecting and reselecting lines frequently. Rather than manually reselecting, create a layer from your selected features to make it less tedious to select the lines you are adjusting.

Good luck and I hope your adjustments go well.