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PLSS not aligning with city boundaries

tmo

I have PLSS data that is supposed to line up with a city's easterly boundary line yet it does not.

There is about a 70 foot gap between the SWSE western quarter section line of the SE quarter of section 31 and the City of La Verne's eastern boundary section line.

My POB is the south quarter corner of section 31 of T1N R8W.

My data frame properties and projected coordinate system for all data is in NAD 83 California V FIPS (V for LA County).

The polygon's western border line was drawn up from where the south quarter corner of section 31 lies.

This northerly running line that transects section 31 is also the SWSE's western line of the SE quarter of section 31 yet they do not align with the city boundary which according to the tract map is all supposed to align together.

I have contacted the engineer working on this parcel and he instructed that he is going off the tract map and that the GIS data is wrong. It is wrong but I'm not sure if that is my doing or the data itself.

Attached is a photo.

After drawing up this polygon I am supposed to combine it with the city boundary and detach from a polygon not shown. I am going to simply align the polygon up with the eastern boundary line of the City of La Verne and merge them together.

I would like to avoid moving the polygon and have the parcel draw up and the lines aligned properly otherwise I will have to use the workaround of moving the polygon west and merging.

Screenshot 2022-05-05 170306.png

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jcarlson

Where is your PLSS data from? And where is your parcel data from?

I work with PLSS data and parcel boundaries near-daily at work, and I can tell you that the PLSS layer provided by the State rarely lines up with the parcels. In some areas where the PLSS corners are poorly documented and the deeds are from the 1800s, it's actually quite common to see offsets even bigger than the one you're seeing.

tmo

Hi Josh, thank you for your reply.

My data is from the BLM website and has also been checked off of the data from the California State Geoportal website.

The city boundary layer is from the LA County GIS enterprise hub.

I spoke with the surveyor and he stated that the GIS data often times is incorrect.

From our discussion I was going to assume the GIS data was inaccurate and trust his assessment from his survey and review of the plat map for this area. Leading me to arbitrarily move the data to the west.

jcarlson

Even if it feels arbitrary, surveyor data is typically the most reliable, at least in my experience. If the surveyor in question is willing to share coordinate information, that's often the very best.

tmo

Do you have any advice in mind for this gis inaccuracy phenomena?

And by coordinate data are you referring to the northing and easting? I do sometimes receive those and they are godsends.

jcarlson

Yeah, the northings and eastings.

By chance are you using a parcel fabric dataset? There are some good workflows out there for adjusting a parcel fabric based on known reference points / adjustment links.

We have quite a lot of "bad data" spots like this in our parcel data, for all kinds of reasons. (Look up the "Indian Boundary Line" related to the Chicago Portage / I&M Canal for one of them.)

The way we are working on this issue is to review our surveys, plats, and monument record documents on record and pulling out any PLSS corners with coordinates. We have been mapping those corners as points.

Once we have two adjacent PLSS corners with good coordinates, we can draw a township/section line between them, and we know that all parcels along this boundary (unless otherwise specified in their legal descriptions) should align with it.

Performing the adjustment itself can depend on the size of the offset. If it's only a couple feet, I will simply snap my parcel features to the line. If it's a bit larger, as in your post, you'd want to somehow distribute the adjustment across multiple parcels proportionately. That's where the parcel fabric tools, such as the aptly-named Adjust Parcels, come in particularly handy, but there are other ways to do it, too.

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