In my local area (USA/Florida/Gilchrist) they have by tradition driven a railroad spike into the road pavement as a survey starting point. The railroad spikes are easy to locate, because the surveyors must dig a small square opening in newer pavement to expose the spike. These are used primarily for surveys, but also are conveniently located at the middle of many road intersections. These type of points, combined with the GPS fix, will be useful for correctly locating the highway center-lines.

I have taken one GPS fix on such a spike, and uploaded it as a test, with these tags …

(object # 3656650954)

  1. Is this the preferred tagging for this object ?

  2. Are there any other tags I am missing ?


I think this is more of a local question. Triangulation points, in the UK, are used by Ordnance survey, tend to be at the sides of roads, or even open country, and are several miles apart. They are likely to have been re-surveyed within precision DGPS systems, although that information cannot be used in the UK. In my view, if they don’t appear on an official state or federal database, they are probably not equivalent to UK triangulation point, but local usage may mean the tagging is still reasonable.

If you are making GPS measurements on such objects, could I suggest that you take a reading averaged over a long time, rather than a single reading.

This is what is meant by this tagging in a UK context: In the UK they are now only of historical interest:

I doubt that a triangulation point in the US would be installed in the road. Too much chance of it moving a fraction of an inch as pavement, especially asphaltic bound macadam (blacktop, tarmac) which can flow with heat and traffic loads.

Way back when I worked as a “summer engineering aide” on a highway department survey team in the days of “chains” (at the time just a fancy tape measure) and transits we used nails driven into the pavement for temporary local reference points.

For anything with serious accuracy (better than a 100th of a foot) we’d work our way in from a benchmark. Benchmarks were always located on things that were less likely to move around than pavement, often massive concrete items with deep foundations like bridge abutments.

It is my understanding that actual triangulation points (not just a generic benchmark) are very much more accurately measured and tracked by the geodic survey people than anything being done by normal land survey teams.

Perhaps calling this a triangulation point is a poor choice of terms. Up until GPS became widely available, these were used regularly when surveying private property, as a stable beginning point. One generation of surveyors would use existing spikes, as referenced from previous surveys.

Digging thru the 1973 Manual of Surveying Instructions (US DoI/BLM) of the various types of monuments, the Reference Monument seems the most likely candidate. I will have to go look at one of these spikes, to see if there is an “X” stamped into the exposed head. Not all of these are located at Section corners, but some are.

have a look of

grüße von lutz

One additional thought … I had been of the view that most of these spikes are at road intersections, but one is not (that I am aware of). Then I remembered that there once was an unimproved side road at that location. It has since been abandoned, possibly 20 years ago. The earliest road files loaded to OSM (likely based on old census files) actually showed that unimproved road. What was once a pair or tracks thru the dirt, used by school buses, is now abandoned and fenced off. So all the spikes are at what was once road intersections, and were probably placed in the roads 50-60 years ago.

This county is small and has no survey department of it’s own. At one point these roads were state maintained. Either state survey crews placed these spikes, or private surveyors (working for the county) did so. They then used them as beginning points for surveys, on lands adjacent to the roads.

The two spikes I examined yesterday had markings on the head, but those marks were likely of the spike material and manufacturer. I did not see an “X” stamped on the head. Due to several layers of road resurfacing, the spike heads are now 2-3" down in a small hole (which has to be exposed after each new layer of asphalt is applied).

head of railroad spike, in pavement. found this morning on an adjacent road that gets much less traffic than the road I live on. The pavement over there could be 30 years old, or more. There were 4 on that road, all on the center-line.