Who are those surveyers in the street?

Factual Questions
1

I call them surveyers but I really have no clue what they’re up to.

You might have seen them, clad in bright colored vests and hard hats. They tend to set up a tripod with a telescope in the exact middle of an intersection, then spend an inordinant amount of time peering through it. Sometimes theres another tripod set a distance away. When I was in college, they’d sometimes have these tripods set up on grassy hills, roads, or sidewalks

Does it have something to do with measuring how straight a road is, or measuring the distance between 2 points? I can’t see how a telescope or whatever that thing is would help in that respect

2

They are probably surveying the area as a prelude to improvements by the city. See here for an example request for proposal.

3

What you describe sounds like an engineering survey (map prep) or a topographic survey (distance and elevation).

The telescope has measured crosshairs in it and a surveyor’s level on top.
The level keeps the telescope (it is REAL powerful) horizontal.
The thing at the other end is probably a range pole.

There is GPS survey equipment that are very accurate.

4

Thanks for the info, but that brings up even more questions for me :confused::confused:

  1. Why would they need to resurvey streets that have been around for decades? Especially in such a seemingly hazardous and low-tech fashion? Google Earth just drives a car around with cameras!

  2. Why always in the middle of a street? Why not on a sidewalk?

  3. Aren’t satellite photos enough?

5

I’m not a surveyer and am not qualified to answer your questions. Let’s be patient and let the Straight Dope do it’s job.
Probably more information about what’s going on in that neighborhood would be require.
Until a qualified surveyer shows up, I’ll make a WAG that somebody may not have performed proper maintenance of land records, or over the years a lot of land may have changed hands and the old information is being challenged.
On the other hand there may be some new zoning plans underway and part of the deal requires a resurvey.

6

Are they also spray-painting marks on the street?

They may be measuring exactly where underground sewer pipes / electrical lines / etc run under the street prior to digging it up for repairs/maintenance of same. At least that’s what tends to happen around here.

7

I didn’t notice any spray markings but I have noticed some construction further down the street. Hmm…

8

Topo maps are now done by Aerial Photography.

9

They might be surveying almost anything. Sometimes a modern survey requires returning to a known reference point and continuing from there. I just had a survey done for a piece of property I was selling, and the surveyor had to go back about 3 miles to find one of the required two reference points to start. He was nowhere near the property at that point.

Old surveys were often poor by modern standards…“starting at the brown cow by Mrs. O’Leary’s oak tree, traverse 3 chains and 4 rods north-northwest to the big black rock with ice all over it…”

10

A good friend of mine used to be a surveyor for the city. You’d think that since the city has been here for a few centuries they’d know where the damned water lines are, as they put them in themselves. You’d be wrong. Especially in an old part of town where anything could be down there. Pretty much all the work they did was in town marking utilities before construction. The maps they had were old and/or unreliable, and hitting a gas pipe is expensive AND dangerous.

ETA - in a major streetscaping project, there was a huge delay because one of the buildings, which has been there since, I dunno, the 50’s or 60’s, was discovered to have no foundations. At all. It was resting on the sidewalk in the front, essentially.

11

Civil engineer here.

I have surveys done all the time. You need them for any improvements done to roadways and for below-ground pipes (water, sewer, etc.). This includes roadway reconstruction, replacement of aging sewer or water pipes, etc. If I’m designing a new sewer, for instance, I don’t want to have it go through an existing gas main or water main.

Records for existing infrastructure (including water, sewer, gas, telephone and electric conduits, etc.) are often sketchy. Also, roadway improvements (repaving and curb replacement projects) often change the elevations and horizontal locations of road features.

Most large cities have base maps that are periodically updated. Smaller municipalities often do not. For a given project, if I have no existing base map at all, I will often commission an aerial survey, in which an airplane with cameras produces a topographic plan of the area, along with curb lines, etc. If I already have a base map, I can skip this step.

In any event, you then need surveyors on the ground to pick up the locations and elevations of critical features, including the curb line, crown of the road, manholes, water gates, electric vaults, telephone vaults, etc. This information is generally surveyed to the nearest 0.10 foot. For some buried features, we also have to conduct test pits to figure out where some lines are located.

Invariably, when we try to go to construction without a recent survey (as a cost-saving measure) we end up with innumerable conflicts. It’s always a good idea to get a good, recent survey before starting a major construction project.

Oh, and modern survey equipment usually include what are called “total stations” that use laser rangefinders, etc. to determine the precise distance and elevation from the base station (i.e. the tripod) to the rod (which has a laser reflector). From one known point (referred to as benchmark), you can determine the distance and elevation to any other point within visual range.

In generally, aerial survey (not to mention truck-mounted cameras and satellites) are not nearly precise or accurate enough.

12

This is a related question that I have been meaning to ask: as I walk around, I see round metal objects about the size of a nickel in diameter embedded flush in the street and sidewalk. On my dog walk the other night, there were several in the sidewalk along a very short stretch, and they had small rings painted around them in white paint. What is the purpose of those? If they are surveying marks, why do the need a bunch of them in a small section of sidewalk?

13

Thanks robby, that pretty much totally answers my questions!

14

They sound like survey control points (i.e. a point of known location and elevation referenced back to some benchmark). They act like intermediate benchmarks, so you don’t have to go all the way back to the original benchmark.

I have no idea why they would need several of them in close proximity.