How did they do topographical maps before modern computers and satellites?

[GusNSpot]

Kelsh projection stereo plotter. I have actually used one of these to make a for real map … ( also a 3 projector K&E, Ziess PG 2’s & 3’s. ) I was in the Mapping business from 1970 to 1998. Mostly as a pilot, ( about 8000 hrs as PIC doing actual mapping work ) surveyor. plotter operator, photo lab worker which also made me a LogE contact printer operator.

Did all manner of projects. the only thing I could not do was to ‘scribe’ a finished product negative that was then printer on velum to be given to the client. I just did not have the ‘touch’.

Have used cameras ranging from 5", 7" 9" formats with camera of 3.5, 6.0, 12 & 24 inch focal lengths.
Fairchild T-12 WWII era to Ziess RMK TOP Cameras in auto mounts using GPS airborne & ground data.

Surveyed with old Chain & pins & a dump level to full 'total stations, & was in the GPS stuff from the beginning back when there were only 3 satellites max in sight & still had the military ‘jitter’ that had to be worked around.

A lot of maps are still done this way, aerial mapping for a specific job at altitudes of 1200 to 12,000 feet depending on desired final product.

The new laser stuff is wonderful for many things but not for everything. Satellite imagery is the same.

Back in the 1800’s when the government surveyors were counting wagon wheel turns and setting center of section stones. they did very impressive work considering everything.

I do not know about other stated but a lot of sections in Oklahoma still have “GOD” rocks, center of section markers laid down at the first survey in the 1800’s. Yeah, they crossed Indian territory back then too.

In legal fights over land surveys, the ‘GOD rock’ is GOD. No matter the new accuracy in modern tech, if it is based on the ‘GOD rock’ you win.
They are ground zero.

Also remember, map producers, especially with automatic computer doings, 95% + do not delete old trails & roads outside of cities, they just add more new stuff. Right where I live in Arkansas the latest maps, Google Earth, 7,5 Minute Quads from the government show a road that has not been used since 1910 and can only be followed with difficulty on foot. It is shown the same way the present road is. Confuses strangers no end…

Map making is not so cut & dried nor exact in many places as one would think. The fact that they are as good as they are in many hard to reach places is what is amazing.

If you could see and check on the ground the differences in 1 foot contours between computer generated maps & one drawn by an experienced Photogrammetrist, you will see why the human map is better.

While surveying our crew found more than on USGS benchmark off by lots. We would do a few more level loops and some trig elevation checks from other well used & proven bench marks, send it all to the USGS and would eventually re-survey and redraw the maps. But it is government, it is a slow process.

Some on who has many days of boots on the ground will know better what the actual ground does than a computer can know so in places that can not be seen, the human is more likely to be correct than the computer.

Also see, ‘Soil conservation’ mapping and map production from the 50’s & 60’s. Done that also…

YMMV snerk I just had to do that,…

[Kron]

@Heracles

I was under the impression that (from the 19th century at least) they had human surveyors actually walk the terrain and measure the elevations all over the place (as in this movie). And, at the same time, setting official milestones that could be used for locating and sizing lots for legal / title purposes. Is that mostly a fairy tale?

That is absolutely correct. In the Public Lands Survey System in the United States, most of the country is blocked out into 1 mile sections, with additional markers at half-mile increments, and occasionally 1/4 mile increments as well. They were originally done with what materials were available to the on-the-ground surveyors at the time (native stone with marks carved to identify the stone, or trees scarred with identifying marks). Eventually the General Land Office (the precursor to the Bureau of Land Management) began resurveying the townships and replacing marker stones with 3-inch brass caps set on iron pipes, with all the identifying marks stamped on the face of the cap, like this.

I have spent a lot of time on the ground searching for those, as a surveyor here in Northeast Wyoming. Nowadays, I spend all of my time making maps, having switched my focus in the company I work for to GIS (it is a lot warmer in my office in the winter!)

[SlackerInc]

So I’ll confess I don’t understand how elevation was measured in the analog era. I looked up altimeters, and Wikipedia says that since air pressure changes as the weather does, they have to be periodically recalibrated with “points of known altitude”. But how did those points get determined to be a certain elevation to begin with?

[GuanoLad]

@SlackerInc

So I’ll confess I don’t understand how elevation was measured in the analog era.

Like this.

[Norse]

@SlackerInc

But how did those points get determined to be a certain elevation to begin with?

Trigonometry. Sea level is at a fairly constant elevation, and then you just start from there working your way inwards and upwards.

When I was younger, our topographical maps always had a certain symbol for “trigonometric point” (a triangle with a dot inside), and these were located on easily distinguishable topographical features (like, say, a summit that wasn’t easily mistaken for another summit). I guess these were “those points” you’re talking about, and that their elevation had been determined previously by cartographers working their way from the sea with their angle measuring instruments.

I haven’t looked for those symbols for a while, and besides I’m using dead tree maps less and less these days, so I can’t say whether this is a standard feature of modern topographical maps.

[Colophon]

@Norse

I haven’t looked for those symbols for a while, and besides I’m using dead tree maps less and less these days, so I can’t say whether this is a standard feature of modern topographical maps.

They’re still there to this day on British Ordnance Survey maps.
Example. (And on the ground.)

[Mr_Downtown]

Benchmark is the term usually used for a point marked with a known elevation. I’ve never heard trigonometric point. And yes, they’re still on topo maps.

By the way, here’s a convenient way to roam around US topo maps online.

[The_Stafford_Cripps]

@Mr_Downtown

Benchmark is the term usually used for a point marked with a known elevation. I’ve never heard trigonometric point. And yes, they’re still on topo maps.

Well, trig points are very common on any sort of hill in Britain, though I don’t think they’ve been used for several decades. There are also benchmarks which are only marked on large scale maps.

You can see the symbol for a trig point on the first “new map” link in my post above (you need to zoom out) on the hill called “An Groban”.

[VOW]

Trav Points. Because the survey traverses through them.

There are documented, well-coordinated, and thoroughly monumented horizontal and vertical control points. It depends on the level of work you want to do. If you are merely retracing a lot line, you don’t need the amount of precision that a highway bridge or a subway tunnel requires.

With GPS, there are more and more reference points that have been established, with XYZ coordinates obtained via GPS satellite observations. And here in California, you gotta label your work in reference to the most recent ground-moving earthquake. I’ve seen a lot of stuff that is “post-Landers.”
~VOW

[Norse]

@Mr_Downtown

Benchmark is the term usually used for a point marked with a known elevation.

Perhaps it is on your side of the pond. Apparently they’re called trig points even in English on our side

ETA:

@Colophon

on the ground

Somewhat more durable than our type, huh?