# Horizontal control, Vertical control, Cadastral

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I'm attempting to further my education here, so I thought I'd expose my level of ignorance and ask a few questions....

I thought I knew a lot about surveying and the uses of survey marks, but after reflecting on it, I find that I really don't know much about them.

Hopefully some people who know more than I can explain some or all of these things.

Horizontal control and Vertical control marks are aspects of geodetic surveying but Cadastral is not. Geodetic surveying determines the position of points with respect to the Earth's geoid, longitude and latitude. Cadastral surveying only relates to local and distant borders, I think.

Techniques

I think I understand very basically how horizontal control is done - either by measuring distances, azimuths, and vertical angles, or by using GPS, and then using an adjustment program to resolve a net of such control points..

Vertical control also uses the measurement of distances and vertical angles, or perhaps just distances and something else, I don't know. Whether or not angular measurements are used at all is unknown to me. In any case, it is also adjsuted by a computer program to resove a vertical control net.

Cadastral surveying is even more of a mystery to me than vertical control. I can find no explanation on the internet as to how it is done. Certainly distances and horizontal angles are used, but I don't know what's done about the vertical component. Does a property on a mountainside have more surface area compared to the same 'size' property on flat land, or is it the same surface area? I don't know if cadastral surveying can make use of GPS technology. Another puzzle to me is why the central and western U.S. has a lot of cadastral marks while the eastern third doesn't seem to have many cadastral marks. I realize that the borders of the western 2/3 of the country tends to have been laid out on grids, but both the whole country has borders. It would seem that the more complex eastern third would be more in need of cadastral marks.

Uses

It's pretty obvious that geodetic control is involved with mapmaking, and cadastral surveying is involved when property (private or municipal) borders and boundaries need to be established or re-established. Beyond that generality, I'm not sure of exact uses, for instance, if a new building is to be built, is geodetic surveying or cadastral surveying required, or both?

Railroads and bridges tend to have vertical control marks. Is it that no one cares if a bridge is moved downstream a bit by a storm or car accident, just so it isn't any lower or higher?

Is it a grade issue, where car roads and railroads need to be messured in terms of vertical distance for some reason? Are the marks established to help build these roads, or are they established after construction, as some aspect of maintenance?

I can see that if a building is to be built, it must be located well within its proper property boundaries, and cadastral surveying does that, but what then are geodetic horizontal control points for besides making paper (or computer) maps? Do cadastral systems ultimately depend on geodetic control?

Even more obscure

Even more obscure are magnetic stations and gravity stations. Are these remnants of scientific research projects? There are gravity anomalies that warp the geoid but what do these stations do? There's a mountain road vaguely near here that has at least 20 gravity stations on it. There's no mining there anymore, if there ever was much, so what was the curiousity that was or will be satisfied by these gravity stations?

What does a gravity station do that a vertical control bench mark does not do?

Wow, great questions. I can answer (sorta) a few of them, but I'm going to yield to someone with more experience than I. I look forward to seeing your answers.

With the level of understanding exhibited by your questions, you should consider a career in land surveying.

Oh, if you don't get good answers in a day or two, I'll see if the LS I work for would like to take a stab at answering your questions.

I didn't understand any of the questions. However, I am interested about those gravity stations - and one BDT didn't bring up - a Horizontal Traverse station. I rarely see people mention these, and I found my first on my last trip to Colorado.

Black Dog:

I see that Okiebryan has posted your questions on the POB message board....an online surveyor's forum, which should result in some good responses.

I won't attempt to answer all the questions that you've posed, but here's my stab at a few:

Cadastral surveying: Certainly distances and horizontal angles are used, but I don't know what's done about the vertical component. Does a property on a mountainside have more surface area compared to the same 'size' property on flat land, or is it the same surface area?

Usually, for an ordinary property boundary survey, the vertical component is not part of the equation. All distances are reported as horizontal distances and thus areas are horizontal areas (Plane Surveying). Consequently, the true square footage of land surface of a parcel on the side of a steep mountain will be somewhat greater than the "surveyed area measurement." However, a property survey can also include a topographic component in which the elevations/contours of the property are also measured.

I don't know if cadastral surveying can make use of GPS technology.

GPS is increasingly being used in boundary surveying. However, in areas with tall buildings or dense tree cover, the total station is still the tool of choice.

Another puzzle to me is why the central and western U.S. has a lot of cadastral marks while the eastern third doesn't seem to have many cadastral marks. I realize that the borders of the western 2/3 of the country tends to have been laid out on grids, but both the whole country has borders. It would seem that the more complex eastern third would be more in need of cadastral marks.

In the metes and bounds States (Eastern States and Texas), private property was historically described relative to physical monuments (e.g. trees, rocks, streams, roads) and by record monuments (e.g. adjoiners). In the Public Land Survey System (PLSS) States, the Federal Government first delineated the land by marking Township corners, Section corners, and Quarter Section corners. The land was then patented to individuals and described relative to the PLSS decription (e.g. the SW quarter of Section 15, Township 16N, Range 30W of the 5th Principal Meridian). If by cadastral marks we mean mounments to property corners, a metes and bounds State has as many marks as a PLSS State. If by cadastral marks we mean marks set by the General Land Office/BLM marking a Township or Section corner, then of course those only occur in the PLSS States. As properties in the PLSS States get subdivided again and again, the descriptions become metes and bounds descriptions, but with a Point of Commencement or Beginning usually tied to a PLSS corner (e.g. Beginning at the SW corner of S15, T16N, R30W, thence N37d57'13"E to an iron pin, thence...).

Edited by tosborn

Your description of horizontal is essentially correct. While heights can be determined using vertical angles, the most accurate heights and hence the bench marks set by NGS and others comes from differential leveling. You can find some images of Coast Surveyors and NGS crews "running levels" on our history site -- http://www.photolib.noaa.gov/cgs/deter1.html.

Gravity observations are a significant part of the data required to map the shape of the geoid and provide corrections for the leveling observations. Currently there are several ways of observing gravity, including:

absolute and relative terrestrial gravity, airborne gravity and space-based systems such as the Gravity Recovery and Climate Experiment (GRACE). Gravity observations also provide an understanding of the relationship between the geoid and the ellipsoid from which horizontal coordinates are computed by providing the deflection of the vertical which is the angular difference between a normal to the ellipsoid and a normal to the geoid at the same terrestrial point.

Magnetic observations were originally conducted by the Coast & Geodetic Survey but the function was transferred to the U.S. Geological Survey in the '70s. While magnetic observations have numerous applications, in surveying they provided a way for surveyors using a compass to be able to adjust or correct their instruments for the difference between geodetic and magnetic north.

I can contribute a bit on the gravity stations:

They are very important to our Department of Defense and NASA, since knowing the exact gravity gradients in various areas of the earth are critical to proper space (orbital or ballistic) navigation, and other "scientific reasons". Large efforts were undertaken starting at the beginning of the "space age". Of course there were gravity measurements previously, but these measurements, coupled with critical location (i.e. accurate geodetic position) had just become more important. I have seen gravity stations more commonly near DOD or NASA installation. BDT: Any near such facilities near your gravity station grouping?

Above is a very short summary (by me, no research) of a very complex subject.

(BTW: Happy Veteran's Day to the other Vets out there!)

EDIT: DaveD beat me to the punch on gravity, and with more survey related details (thanks!), but I'll stand by the above as well.

Edited by Klemmer & TeddyBearMama

Okiebryan - Heh, thank you for posting those questions on POB. Hopefully people there will enjoy answering some of them. If they do, could you provide a link?

foxtrot_xray - I take it that a horizontal traverse station is a secondary kind of horizontal control - based on a more rigorously set mark, but I don't know.

tosborn - Thank you for answering some of the questions. Hopefully this topic will get a pretty good assemblage of such answers.

DaveD - interesting lore about gravity and magnetic stations. So those are for mapping those creepy magnetic lines and geoid waves. By the way, the URL you gave doesn't operate.

Klemmer - ah more interesting lore - the DoD and NASA connection - for navigating the crazy geoid, eh? I don't think there's any such thing there. Just some very old mountains - perhaps someone was wondering how deep they go or something.

I think we have a contributing member here in the forums.

So fine, but what is Cadastral really? The term comes from Latin base term Cadastre referring to a registry of lands. So actually Cadastral Surveying is surveying having to do with determining and defining land ownership and boundaries.

In my opinion or the way I see it.

The NGS marks are the 1st order of marks.

Surveyors use them for more precise surveys of lesser grade 2nd,3rd,4th and so on down the line.

I use them for plotting from a known well defined point within a system or area.

But I am not a surveyor so it is just a learning process for me.

So one deals with the shape of the Earth NGS and Cadastral has to do with Ownership of land.

Edited by GEO*Trailblazer 1

Your description of horizontal is essentially correct. While heights can be determined using vertical angles, the most accurate heights and hence the bench marks set by NGS and others comes from differential leveling. You can find some images of Coast Surveyors and NGS crews "running levels" on our history site -- http://www.photolib.noaa.gov/cgs/deter1.html.

As always Dave is the source of great information,

One thing I would add, however, is that for mapping (mostly a USGS job), the use of stereo aerial images was until recently (when satellites, GPS etc. came into use) the best way to get accurate topographic information. This, in short, is what you need to make good topographic maps (aka contour maps). However, as with any system like this , you need control on the ground, which is where the benchmarks (both horizontal and vertical) come into play. These points "pin" the undulating surface features produced from the aerial photos at real points on the ground so the mountains and valleys are in the right places and at the right elevations.

In a way surveying is similar: a project will have plans for a shopping center, say, which includes placement of all buildings, parking lots, drainage, utility lines, etc. etc. and the surveyors on the ground will spend their time laying it all out. But they must start with control, i.e. a known location and a known elevation (i.e. Benchmarks). You don't want the water lines in the new Walmart to be 3 inches (or any amount, really) up down or sideways from where the city water lines come in.

And at some point, cadastral and geodetic systems must come into contact so that various systems can match up. The days when townships were laid out in the west and farms and homesteads were built - without regard to their geodetic locations - has faded into history. The widespread us of GPS equipment in the industry today almost guarantees that. I'd love it if one of the professional surveyors on this forum might comment on this. In other words are cadastral and geodetic surveying tending to merge in today's world?

To paraphrase the old NY Telephone commercial "It's all connected ...".

There are a whole series of articles on surveying on the NOAA web site honoring the 200th Anniversary of the U.S. Coast & Geodetic Survey. I’ll list a few of these:

http://celebrating200years.noaa.gov/founda...al/welcome.html (“The Foundations of the National Spatial Reference System’), (Also see the sidebar, “The Geometry of Making Surveys” in the right column.)

http://celebrating200years.noaa.gov/founda...ng/welcome.html (“A Brief History of Leveling at the NGS”)

http://celebrating200years.noaa.gov/founda...ys/welcome.html (“The Downs and Ups of Gravity Surveys”)

http://celebrating200years.noaa.gov/founda...sy/welcome.html (“Entering the Space AGe: The Evolution of Satellite Geodesy at the Coast and Geodetic Survey”)

http://celebrating200years.noaa.gov/transf...al/welcome.html (The National Spatial Reference System Takes Flight: 1987 – 2007”)

http://celebrating200years.noaa.gov/transf...od/welcome.html (“Height Modernization - Leveling the Nation”)

http://celebrating200years.noaa.gov/transf...ps/welcome.html (“GPS: Nouvelle Survey”)

See the many links in the right column of each article.

GeorgeL

NGS

As a recently retired Cadastral Surveyor with the Bureau of Land Management with significant experience control surveying as well as licensed land surveyor in several states I will add my explanations to the list.

Until the last 15 years or so, property boundary surveying has been largely independent activity from control or geodetic surveying. There are also construction surveying and other specialties. The disciplines can overlap, but are different to such a degree that it is possible to have them be separate activities. Land Surveying as a profession may involve these and other disciplines.

The typical land surveyor probably is mostly involved with creating, describing and locating land boundaries (property surveying) as well as laying out things like buildings and other infrastructure on the ground so that they can be located and built where they are supposed to be (construction surveying). With the evolution of GPS as a surveying tool, and a geodetically based survey tool, the property survey has become much more related to using geodetic surveying and the geodetic network than it used to be say before 1990.

The term Cadastral as mentioned above is not a term that is commonly used in the U.S. but refers to property boundary surveying. To be specific the term ties it to property ownership and often taxation as the term was originally intended.

In the U.S. the term Cadastral has traditionally been used for the Federal Surveys that establish or restablish the Public Land Surveys. That was originally the General Land Office whose functions were combined into the Bureau of Land Management in 1946. This BLM use of the term is probably just an accident of history. Today you find many private as well as public land surveyors that are comfortable with the term and may use it to describe themselves in relation to property boundary surveying as opposed to construction work or other aspects of surveying.

Another example of a subdiscipline or specialty within land surveying, and most often a state government function is route or highway surveying that can involve power lines, pipelines, canals, etc.

I sense from your question a request for a deeper explanation of what the differences are between common boundary surveying and geodetic surveying. That would be difficult to convey in any very complete way in a few pages of text. Let me try to briefly review some historical context.

Individual ownership of land started to evolve in the 1400-1800 timeframe. Once private ownership of lands was possible, it became necessary for boundaries to be established, described or located to a larger degree than previously . Prior to that, boundaries existed for the state, king, or feudal owners lands, or for use purposes such as farming.

Let us look at colonial era. Lands in many of the colonies were granted by royal grants to individuals or groups as proprieters. These people could then convey lands to others, or cause towns to be created and lots conveyed. So it is that the large tracts of land that initially constituted the colonial grants were broken down into large estates, then smaller farms, towns, and so on to the current day. In general all these properties would have been surveyed. In the colonial era the primary instrumentation was the survey compass and the gunter's chain. Descriptions were written by a combination of what we call metes and bounds. Mete means measurement, and bounds describes physical features such as creeks, ridges, roads, etc. The lands were then conveyed, divided, conveyed again, etc. to the current day.

Remember that virtually every property in the country has been surveyed and it's corners monumented at some time in it's history. There are a few exceptions where the boundaries may be defined in records only having never been established on the ground. It is usually the case, though, that at some point as the land is sold or inherited over time that a survey of it is performed.

In the 18th and 19th century measured survey lines were most often described with bearings measured with a magnetic compass and distances measured with a surveying chain held level. By the end of the 19th century these methods were rapidly giving way to the use of the surveying transit and the steel tape for measurement. Distances measured with a tape may be have been performed by holding the tape level, or by determining the horizontal component of the tape on the slope with vertical angles measured byt the transit or a clinometer. During the 1970's this changed quickly with the advent of digital technology, the calculator, the electronic distance meter and digital theodolites and total stations.

A line on a boundary described as being 1000 feet long, means it is 1000 feet as would be measured horizontally and not up the incline of the land. Areas reported for land are similarly based on the horizontal equivalent of the boundaries.

States regulate land surveying in their state and issue licenses to surveyors based on experience, education and testing. Each state has a statute which defines land surveying, and most often the differentiating aspect in their definition is the establishment or location of property boundaries. Generally the county is the location where survey records are kept, but there are survey records in state agencies, federal agencies as well as in local surveying companies.

These individual surveys and monuments are less noticable to the public. Old surveys may have had corners marked by stones, mounds of stones, or by wood stakes, calls to trees and other things of a more temporary nature. Metal monuments were not commonly used until about 1900. Most local surveys are monumented with pipes, iron rods or sections of rebar today. These may not be marked in any way, however some states require a cap or other marking to identify the surveyor who set the monument.

Land boundaries are more a hierarchy of the chronology of how the lands were divided and land surveying often involves a lot of historical records research as well as finding evidence of previous survey lines and monuments on the ground.

You may live in an urban subdivision whose lots were laid out and surveyed in 1980 with electronic total station and computer generated coordinates, or in 1950 computed and drafted by hand and laid out with a transit and tape. That subdivision may have been cut out of part of a larger tract of agricultural land that was surveyed in the 1930's cut out of a larger tract of farm land. That farm may have been created in the 1880's surveyed with compass and chain, and so forth.

Outside of the original colonies there was a lot of land that was originally federal public domain. This began when colonial states relinquished their claims to western lands as part of forming the United States and the sale of those lands being to help support the central government. A system was set up to survey, describe and sell those lands in 1785 and it began in Ohio. These are the PLSS or so called rectangular surveys which consist of townships and sections. Land title in most of the non colonial states is based on them. There are a few states such as Kentucky and Tennessee which had so many state land claims in them that the rectangular system was never fully implemented, although there are township surveys in Tennessee. The public land states, besides the early midwest include the south from Alabama to the west, Florida, and of course everything to the west. These lands were surveyed and patented to individuals by the United States and almost all title derives from and is surveyed in relation to original surveys performed for that purpose.

Property boundaries in this country are not generally related to their absolute position on the ground, but relative to local features and monuments. As a practical matter, they were not usually tied into control surveys until more recently, say from about 1970 onward. Route and highway surveys were more often tied into control survey horizontal networks as a way to check them over large distances. In fact one of the early reasons for densification of the control network was to assist in such work.

Well I better quit there, since I have rambled on long enough, but hopefully provided some useful information in response to your question.

- jerry wahl

Edited by jwahl

Okiebryan - Heh, thank you for posting those questions on POB. Hopefully people there will enjoy answering some of them. If they do, could you provide a link?

The Link to the answesr that have been posted on POB. Some good answers here, and over there.

Wow, great answers by Jwahl! I'm enjoying this discussion immensely!

Apparently no comment on the railroad marks, so I will add my 2 pence to point out that I suspect (I'm not a railroad man, just using logic) that the marks (mostly rivets) placed by railroads were to document the grade of the roadbed. I do know that grade is a very important subject for railroads, and I'd guess that even projected operating costs are based on the grade of the line.

Railroads and bridges tend to have vertical control marks.

Once upon a time that was the easyroute to follow for the level crews. Roads did not exist in most areas and thinking at the time was RR's would be around forever.

Apparently no comment on the railroad marks, so I will add my 2 pence to point out that I suspect (I'm not a railroad man, just using logic) that the marks (mostly rivets) placed by railroads were to document the grade of the roadbed. I do know that grade is a very important subject for railroads, and I'd guess that even projected operating costs are based on the grade of the line.

I know that at the first the Railroads owned every other section of land.

This was to encourage and to expand the western territory.

It is also why there are many towns that are on the railroads.

They sprang up after the RR went through and afforded places to stop (Whistle Stops).

I have seen many of the old RR maps from the 1800's.

They would survey through take the best course for the RR and sell the remaining or trade tracts to have a continuous tract of land.

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