California Surveyors Forums

I am developing an article regarding anticipated errors on subdivision maps and would like to know if anyone who reads the following agrees. if not, what are your thoughts?

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Because of the manner in which older maps were prepared and the relative value of land, certain map closures can be expected. Unfortunately, many surveyors spend countless hours running maps and surveys out to the nearest hundredth of a foot, failing to recognize that the map itself didn’t close within half a foot. The expected closures and errors anticipated to be found in the field are as follows:

2000 – Present Plus or minus 0.02’

1980 – 2000 Plus or minus 0.05’

1960 – 1980 Plus or minus 0.1’

1940 – 1960 Plus or minus 0.3’

1930 – 1940 Plus or minus 0.5’

1900 – 1930 Plus or minus 0.8’

Prior to 1900, variances are unpredictable. As many parcels were subdivisions of sectionized lands, the misclosures inherent with federal lands are reflected in these older maps.

interested in where you came up with the your tolerances. This may be ok in the urban environment but in the world outside of paved streets, not realistic. In a rural area 0.5"+/- may be acceptable, depending on how far you came to get there.

It also is dependent on the methods used. I am suspect of any survey that claims 0.02'+/-, as i question if most surveyors use the methods to backup such claims. Most private work does not provide for the time to use the methods and redundancy necessary to ensure such results. Is the traverse closed? is the gps network remeasured at different times of the day or days of the week?

Does the survey stand up to an analysis of the data to prove such claims?

just my 2 cents.

Let me clarify. These are considered reasonable errors of closure when traversing a map. Today we would find 0.02' acceptable. Older maps close by the values I suggested. They are map misclosures and not survey values.

Why shouldn't a map close flat?
The survey data should be adjusted/corrected by the person who did the field work, not the map checker.

I was told by a certain city early in my career (that's 1972-ish) that they required 1:100,000 closure "with today's modern instruments".
So, I took my modern electric erasure and changed a long line by 0.01' and it closed 1:100,000+

again, depends on the project. A map of a USFS multi section boundary survey that covers several miles will not close within 0.02', due to significant figures. The standard for cadastral projects is 1:5000, used to be 1:300. 0.02 over a distance of 5000 is a precision of 1/250,000. Who surveys to that precision? I don't and never will for that type of work. Does GPS give a positional tolerance of 0.02', maybe, not likely without using the correct methods, which due to time and economics and need.

as an example traverse the boundary of a square 5 ac. parcel, 466'+ to a side, a misclosure of 0.1 = 1/18,668. is that acceptable? in my world it is and I'm betting for most rural areas it is. is 0.02' abtainable? 1/93,338, maybe, is it practical, maybe not.

We need to be realistic when setting standards. It is not a one size fits all.

The proposal neglects to address those maps that include the anticipated misclosure due to convergence of the meridians as performed by those whose surveys are geodetic in nature and based on astronomic north and ground distances.
Also for all those other surveys based on some form of a grid based system, misclosures are based on a ratio of overall distance, not some numeric one size fits all constant ignorant of lot, block or overall size.

Let me try again as I think you folks are missing the point. Years ago, many maps showed the bearings to the nearest minute and distances to the nearest tenth. I am looking at a map from 1907. The values are shown to the nearest minute and tenth of a foot. That used to be fairly standard. Over time, with advanced calculation tools, they were shown to the nearest second and hundredths of a foot. Utilizing these significant value figures, running a conventional traverse, you would expect certain tolerances over the years.

THIS HAS NOTHING TO DO WITH MEASUREMENT.

The notion has to do with the inherent accuracies of the underlying maps It has nothing to do with forcing a closure or anything like that. It only has to do with the raw closure of a map.

This analysis does not involve any surveying. It only has to do with looking at maps and nothing more. It has to do with auditing the underlying map - no adjustments - no surveying. it involves trying to figure out of the geometry of the map closes.

Here is a brief outline of the basis for the question:

https://engineering.purdue.edu/~asm215/ ... vcalc.html

I am assuming everyone has tried to close a map.

If the angle is to the nearest 15 minutes, then I can pick any bearing within say 7 minutes of that value when I am trying to 'reverse engineer' the geometry of the map. Taking that principle into account the maps probably close better than we normally get when we just type in what is written.

That being said, what I am saying agrees with your numbers.

Thanks for the observation. Basically, what is the map closure if we input the raw data and attempt to create a closed geometric shape. Modern maps close very well. 100-year-old maps do not. My thesis is simply this: over a 100 year period, what are the anticipated closures of maps from the 1920s, 30s, 40s, 50s, 60s, 70s, 80, 90, and 00s?

It leads to the anticipated deviations one should expect from an older map versus a new one. That is it; it is to demonstrate that these misclosures are generally associated with eras and epochs. The problem is many modern surveyors get caught up when they are dealing with a 100-year-old map and things not fitting. If the lots do not close by half a foot, don't lose any sleep chasing half a foot as it could be anywhere. Follow the footsteps! Before starting a survey, check the map out to see how well it closes before starting the survey.

The attached outline is part of this discussion. Does it make sense? Does anyone have a better approach? Would this function as a reasonable standard of care or custom and practice?

I'm not sure there's a lot of value in trying to characterize misclosure quantities based upon map age, at least not statewide. I think it depends more upon who made the map than when it was made.

You are trying to precisely quantify something that has wildly varying variables.

Thank you for your comments everyone.

Out of curiosity, have any of you done any forensic surveying or forensic analysis on maps and documents as distinguished from conventional land surveying? This involves evaluating a map, field notes, deeds, records, etc. to determine if these documents comply with the standards that prevailed at the time they were created? It is a legal process used to grade or rate the material under consideration. A forensic surveyor can explain and describe the difference between two maps,100 years apart and what the process was used to create both of them and what the expected accuracies are. It is part of error analysis and weighted error distribution. As Jeff Lucas says: "Forensic land surveying is the "application of surveying" and engineering "science to the elucidation of questions before courts of law and equity."

That is the context of the questions.

There are clearly differences in maps.

I hope that places the analysis in context.

Interesting. I wasn't aware of any such formal process. It seems to me that any boundary survey would/should contain elements, at least informally, of forensic map or deed analysis.

Yes, it is a separate area of practice. It is pretty interesting. My inquiries are in context of something different.

Olin, did you get a chance to review my standards for doing a boundary survey? In a court of law, there are usually some standards that are used or what is known as "custom and practice." Do you believe what I compiled is a reasonable outline?

Many states have minimum standards. Do these make sense? If not the attached outline, are there any standards you are aware of?

IIRC allowable error of closure is determined by the length of the traverse. If you use a hard number such as 0.02' then trying to get that closure on 1000 acres vs 1 acre is near impossible.

Many old maps do not close. I have seen town plats where if there is considerable error between the overall length shown and the sum of the individual segments (lots and streets).

Mike, I think it's a thorough overall outline that also includes some helpful details. I particularly like your point that by asking neighbors about unrecorded documents that they may be estopped from using them later if they didn't provide them when asked. I am going to keep this in mind.

The document does a great job in outlining the extents of what may be required of a surveyor in certain situations. The concept of sufficiency is key to determining the extent of research and field work in any given situation. Of course this would have to be determined on a case by case basis which I assume the courts would do.

I'm not aware of any guidelines for surveyors outside of maybe the BLM book, this would be a valuable thing to have.

I would add that if there are street improvements that are believed to have been built at or near the time of the original subdivision, their location should be measured and compared to the other evidence.

I would also add that if a survey discloses conflicts between property lines and occupation the surveyor should assist the client by providing options to remedy. When possible, the surveyor should encourage the client and the adjoiner to solve the problem and help with any necessary resolution. If the neighbors choose to work with each other, a map should not be filed until the process is finalized.

I would think that the process would involve examining the mapping itself to determine if an opinion could be formed based upon that examination itself. As you mention some maps show distances to the nearest tenth of a foot. It might be more useful to compare maps from the same era and the same region to see if a pattern of practice is discernible. The precision of the map is one thing and the layout of the subdivision maybe an entirely different matter. Surveying textbooks from the era may be useful to answer the question. I think a chart stating expected mapping precision for certain eras may be subject to mis use and misunderstanding. Thanks for all your great work.

Your expected mapping errors may be valid for a limited geographic area and category of lands. For example, lands mapped and subdivided in urban and suburban areas of Southern California. From past discussions with S. CA surveyors, it seems that there is a longer and more consistent history of surveying and mapping standards that were generally followed by most practitioners as compared to almost any other part of, not only CA, but of any region in the US.

The errors that you list, associated by decades, simply don't apply with any consistency to most other parts of the State, or other areas of the US I have worked in. There are some localized exceptions, generally in more urban areas, or where the physical conditions of the land presented fewer challenges to making good measurements.

Of course, mapping error and actual measurement errors are related but different matters. In some areas, the idea of making adjustments to one's measurements was considered to be falsifying your measurements to make your map close. The arguments and points made would be very much like the more recent discussions of whether or not reporting your measurement to equal record because it's within your realistic measurement tolerances is OK. We have reasonable surveyors that say that makes perfect sense, and we have others who consider it a form of fraud.

That attitude toward adjusting one's measurements to distribute the errors isn't just an attitude that some surveyors had 100 years ago. There were many seasoned surveyors around during my first few years who held that attitude, and there are still a few who have yet to fully retire holding that attitude. It was/is more prevalent in some regions than others. Although it is ever more common that the information shown on final maps is reflective of adjusted measurements and/or calculated values based on adjusted measurements, in some regions, and as to some individual surveyors, the "measured" values shown on final mapping is more reflective of raw field data.

Difficulty of making accurate measurements due to terrain, weather, or other usual and normal conditions is a major factor in expected errors in previous surveys, and depending upon the particular region or locality, to a lesser extent, the expected mapping errors.

The care or skill employed by surveyors in making adjustments varied quite a bit in some areas, as did (and still does) the level of and skill employed by reviewing parties.

Since the 1980s, most jurisdictions have adopted mapping standards that include mathematical closure as an element. In some jurisdictions and for some low skilled reviewers, that is the primary or only element. Trying to quantify mathematical closure errors and apply those findings to the profession broadly can be done with much greater consistency from jurisdiction to jurisdiction, or region to region with much better consistency because of that.

Prior to about 1980, it's all over the board, depending upon common local physical conditions (terrain & vegetation or other obstructions to measurement), typical level of training for the average practitioner, local standards of practice (the minimum standards are now considered to be by state, region, or in many cases national, but prior to the 1980s, the valid standard was a local standard), and individual skills and habits of individual surveyors. In my experience, these factors have historically made for widely varying levels or amounts of expected errors in the actual surveying and in reporting errors per the dimensions stated on maps.

I often make forensic analyses of maps and surveys when using evidence of those surveys to perform a new survey or when compiling data for informational maps.

First and foremost, the map is evidence of the survey it depicts, it is not the survey itself. If I can also obtain the field notes, I will consider and compare them to mapped info. In evaluating the map, I will consider the precision to which the dimensions are reported, the equipment and methods most likely employed, the conditions under which the survey was made, and sometimes, the reputation of the individual surveyor or organization who made the survey and prepared the map.

When regarding the closure, I analyze whether adjustments to effect a perfect closure results in adjusted dimensions that are within or close to the +/- precision of the dimensions depicted. (i.e. where the map indicates a distance of 150 1/2', the precision is +/- 1/4', and an adjusted distance of 150.68' is effectively the same dimension as reported.) If the misclosure is excessive by this test, then I consider that as being reflective of the care (or lack thereof) that was likely exercised in performing the survey, although field notes are a better indicator of that and, if I have them, are given more weight as to the quality of the field survey.

For retracement purposes, I think that an analysis of expected errors in the actual surveying is more useful. But any attempt to synthesize such standards would need to be increasingly localized the farther back in time one goes. One could definitely not be able to come up with a useful standard that is applicable to all parts of the State, or even to large portions of the State prior to about 1980.

In many cases, similar but separate regions will likely have had very similar standards due to similar conditions, but one should carefully consider the conditions of the separate areas prior to assuming the standards applicable to one also apply to the other.

Evan,

Thanks for putting it to words the points I was trying to make in my short summary. Further more, aren't the monuments the primary evidence, and the map is the supporting evidence?

Yes. Physical evidence of the survey is primary. The map was created to depict the physical evidence and results of the survey.