PLSS-aided North / South Dakota boundary monument placement

An A0-sized poster for SOTM 2024 by Dan Jacobson jidanni@OSM ©2024 CC-BY-SA 4.0

(Background photo: Looking east at North Dakota / South Dakota boundary monument #276, with person at left for scale.)

With the help of the US PLSS many of the remaining North Dakota / South Dakota border monuments still standing since 1891 can be located on imagery and placed on Openstreetmap!

  1. PLSS?

    Yes, the US Public Land Survey System, the starch, the magic glue, the permanent hair spray holding together America's arrow-straight north, south, east, west roads and checkerboard farm fields. Without it... Well, just take a look at the eastern United States.

    Today, for the very first time in Openstreetmap history, the PLSS comes out of the shadows and unabashedly plays a direct role in helping us locate any still-standing of these taller-than-a-person historical monuments, which we then place on Openstreetmap. Steps:

  2. Where to start? East end, west end, middle?

    We'll start on the west end (Montana / North Dakota / South Dakota tri-point, highest numbered Terminal Monument 360M) and work backwards (east).

  3. Choose USGS Topographic Map background layer

    [Image: OSM editor]

    You notice that we have selected the USGS Topographic Map background layer there in OSM's iD editor. You will also notice that we are in luck today: the particular USGS quadrangle we are looking at is showing Monument 309 (309 miles west of Minnesota), at an elevation of 2606 ft.

    Normally we would see the PLSS section line extending north, colored red. But in this case there is a dirt road covering it up.

    We do see the black state line passing exactly through Monument 309, as it should.

  4. Ignore South Dakota

    Back in 1891-92 the monuments along the border were placed on North Dakota PLSS section corners (not South Dakota's!), and every half mile in between.

    Thus even though you see red lines extending both northward and southward from the state line, you need to ignore the southward ones. Same with fence lines: a fence coming from the north might run along a North Dakota PLSS section or half section line. One might expect a monument near where the fence hits the state line. On the other hand, pay no attention to fence lines coming from the south. They would be South Dakota PLSS-based. So, even if you see a bright fence post big enough to be a monument, if there is a tell-tale fence leading southwards from it, discard it.

  5. Place temporary markers every mile...

    In the (iD) editor click on "Point" and place empty points every mile, at the intersections where the red section lines coming from the north, not south, hit the state lime. Do this not for the entire 360 miles (720 markers) but just for one screen's worth, perhaps three markers (three miles).

  6. ... and half mile in between

    How to locate the half miles?

  7. Switch to aerial imagery and confirm monument existence

    So now in the editor (e.g., iD) we select whatever latest greatest sharpest aerial imagery offered, and see if we can locate a bright pillar with a noticeable shadow (depending on the weather at imagery acquisition), somewhere nearby (or even underneath) where we then slide our marker to.

    Alas it's still 2024 and with current imagery most of the time though we can't be positive we really found a monument or just a pile of dung. Wait, people have written travel logs where they sought out every marker...

  8. Toggle between USGS and imagery backgrounds

    In iD be sure to also try CTRL+B, to toggle back and forth between USGS Topographic maps and imagery backgrounds.

    In fact with a steady eyeball one need not use temporary markers.

  9. Insert tags and save

    Amazing, we actually found a monument. We fill out the tags. Something like:

    name=North Dakota - South Dakota boundary monument 276

    etc. (Exact tags are not the focus of this article!) Now clean up any temporary markers, and then save your edit to OSM!

  10. We can even generate link files

    Besides the red lines on the map, the US Bureau of Land Management (BLM), and State of North Dakota also offer downloads of PLSS geometry.

    With clever post-processing of such data, we determined which of the nodes of a section ring were the SW and SE corners, and their halfway points, and created link lists like 359½ 359 | 358½ 358 | 357½ 357 | 356½ 356 | 355½ 355... Clicking on such links brings you to the general location in the OSM (iD) editor where a monument is supposed to be.

    The fact that iD lacks a crosshairs to show the exact position of the URL given can be forgiven, as we don't have a very exact position to give it anyway.

    Take Monument 276, our background photo. Even if there were no weeds and all background layers showed it, they would still be in slightly different positions.

  11. If you get as far east as the Sisseton Reservation

    [Image: Western boundary of Sisseton Reservation]

    Note from mile 44.5 to mile 12 the boundary crosses the wedge shaped Lake Traverse Indian Reservation (Sisseton Indian Reservation on maps), with its different grid and interesting story as to why.

    In the image we computed potential monument points up to Monument 45 (elevation 1631 ft.), whereupon we hit the Reservation's western boundary. We know that the monument at elevation 1714 ft. is Monument 44½, and the one at elevation 1733 ft. must be Monument 44. Now all we need to do is check the aerial imagery to be sure they are still there. (In fact the red PLSS section lines still do connect to the monuments on the Reservation, but they need to be extrapolated from the north, into the Reservation.)

  12. Other uses of PLSS data

    It turns out not only such borders, but even the grid system underlying many cities' streets and their house numbers are PLSS-based!

    The framework, (USA: PLSS, Canada: DLS,) behind all those rectangular roads and administrative districts has been revealed and now is in your hands! (Except Texas: rectangular yes, but not PLSS.)

KMZ of all points. Source code. See also North Dakota - South Dakota boundary marker calculations.