NCPMA
ADVANCED MAPPING
NORTH CAROLINA PROPERTY MAPPERS ASSOCIATION
ADVANCED MAPPING
SECTION 5A
SURVEYING
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5A.1 Surveying
Surveying is the science and art of making measurements of distance and direction necessary
to determine the relative position of points on, above, or beneath the surface of the earth, or
to establish such points. In a more general sense, however, surveying can be regarded as that
discipline which encompasses all methods for measuring, processing, and disseminating
information about the earth and its environment.
Using modern ground, aerial, and satellite technology surveyors can make measurements
necessary to provide accurate property line locations.
5A.2 Geodetic and Plane Surveys
The two general classifications of surveys used in mapping are geodetic and plane. In
geodetic surveying, the curved surface of the earth is considered by performing the
computations on an ellipsoid. In plane surveying, the reference base for fieldwork and
computations is assumed to be a flat horizontal surface. For areas of limited size, the surface
is relatively flat. On a line 5 miles long, the ellipsoid arc and chord lengths differ by only
about 0.02 feet, a quarter of an inch.
5A.3 Specialized Types of Surveys
Control surveys establish a network of horizontal and vertical monuments that serve as a
reference framework for other surveys. Control surveys establish precise horizontal and
vertical positions of reference monuments. These monuments serve as the basis for
originating or checking subordinate surveys for projects such as topographic and
hydrographic mapping; property boundary delineation; and route and construction planning,
design, and layout. They are also essential as a reference framework for giving locations of
data entered in Land Information Systems (LISs) and Geographic Information Systems
(GISs).
Traditionally there have been two general types of control surveys: horizontal and vertical.
Horizontal surveys generally establish geodetic latitudes and longitudes of stations over
large areas. From these values, plane rectangular coordinates, usually in a state plane or
universal transverse Mercator (UTM) coordinate system can be computed. On control
surveys of smaller areas, plane rectangular coordinates may be determined directly without
obtaining geodetic latitudes and longitudes.
Topographic surveys determine locations of natural and artificial features and elevations
used in map making. These surveys are made to determine the configuration (relief) of the
earth's surface and to locate natural and cultural features. From the survey data, using various
types of lines and conventional symbols, topographic maps that depict these natural
and cultural features are produced. Topographic maps are simply graphic representations of
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portions of the earth's surface. Natural features normally shown on these maps include relief
(hills, valleys, and other surface irregularities), hydrography (rivers, lakes, oceans, etc.), and
vegetation. Cultural (artificial) features are the products of people, and include roads,
railroads, trails, buildings, bridges, canals, and boundary lines. Names and legends on maps
identify the features.
Topographic maps are made and used by engineers and planners to determine the most
desirable and economical locations of highways, railroads, canals, pipelines, transmission
lines, reservoirs, and other facilities; by geologists to investigate mineral, oil, water, and other
resources; by foresters to locate access or haul roads, fire-control routes, and towers; by
architects in housing and landscape design; by agriculturists in soil conservation work; and
by archaeologists, geographers, and scientists in numerous fields. Topographic maps should
not be confused with planimetric maps.
A planimetric map depicts only natural and cultural features in their plan positions and does
not show relief.
Land, boundary and cadastral surveys are usually closed surveys to establish property
lines and corners. There are three major categories: original surveys to establish new
section corners in unsurveyed areas that still exist in Alaska and several western states;
retracement surveys to recover previously established boundary lines; and subdivision
surveys to establish monuments and delineate new parcels of ownership.
The latter two are of the most concern to property mappers. Retracement surveys are run
for the purpose of relocating or reestablishing previously surveyed boundary lines. They are
perhaps the most challenging of all types of surveys. The fundamental precept governing
retracement surveys is that the monuments as originally placed and agreed to by the grantee
and grantor constitute the correct boundary location. The objective of resurveys therefore is
to restore boundary markers to their original locations.
Subdivision surveys consist in establishing new smaller parcels of land within larger
previously surveyed tracts. In these types of surveys, one or only a few new parcels may be
created, in which case they may be described using the metes-and-bounds system.
Conversely, in areas where new housing is planned, a block-and-lot subdivision survey can
be conducted, thus creating many small lots simultaneously.
Hydrographic surveys define shoreline and depths of lakes, streams, oceans and other
bodies of water.
Route surveys are made to plan, design and construct highways, railroads, pipelines, and
other linear projects. They normally begin at one point and progress to another in the most
direct manner permitted by field conditions. The required alignment for any proposed facility
will normally have been selected as the result of a preliminary design, which is usually based
on a study of existing maps and aerial photos. The reference alignment will most often be the
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proposed construction centerline.
To stake the proposed reference line, key points such as the starting and ending points and
angle points will be set first. Then intermediate stakes will be placed on a line between the
key points at 100-ft intervals.
In route surveying, a system called stationing is used to specify the relative position of any
point along the reference line. The starting point is usually designated with 0+00. The term
full station is applied to each of these points set at 100-ft increments. A point located
between two full stations, say 84.9 ft beyond station 17+00, would be designated 17+84.9.
Thus locations of intermediate points are specified by their nearest preceding full station and
their plus. In the designation of station 17+84.9, the plus is 84.9.
Stationing not only provides a convenient unambiguous method for specifying positions of
points along the reference line, it also gives the distances between points. For example,
stations 24+18.3 and 17+84.9 are (2418.3-1784.9), or 633.4 ft, apart.
5A.4 Types of Measurements in Surveying
5A.4.1 Pacing
Distances obtained by pacing are sufficiently accurate for many purposes in surveying .
Pacing is also used to detect blunders that may occur in making distance measurements by
more accurate methods.
Pacing consists of counting the number of steps or paces in a required distance. The length
of an individuals pace must first be determined. This is best done by walking with natural
steps back and forth over a measured level course at least 300 feet long, and dividing the
known distance by the average number of steps. Pacing is one of the most valuable things
learned by a surveyor, since it has practical applications for everybody and requires no
equipment.
5A.4.2 Measurements by Stadia
The stadia method is a rapid and efficient way of indirectly measuring distances. It's really
only a quick check of measurements made by higher order methods. These measurements are
taken with theodolites, transits and levels. When you look through one of these devices you
will see a center horizontal cross hair, and two additional horizontal cross hairs spaced
equidistant from the center one.
With the line of sight horizontal and directed toward a graduated rod held vertically at a point
some distance away, the interval appearing between the two stadia hairs of most surveying
instruments is precisely 1/100 of the distance to the rod. Thus, the intercept on a rod held
100 feet away would be 1.00 foot. See Figure 5A-1.
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Figure 5A-1
Transit and historical rods used in surveying
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5A.4.3 Taping
Measurement of a horizontal distance by taping consists of applying the known length of a
graduated tape directly to a line a number of times.
Early surveyors struggled with braced timber panels, wood and metal poles. These devices
resulted in the term pole as a unit of measure. Its length was 16 1/2 feet, the same as a rod or
perch.
A Gunter's chain, (see Figure 5A-2), was the best measuring device available to surveyors in
the United States for many years. It was 66 feet (4 poles) long and had 100 links, each link
equal to 0.66 feet or 7.92 inches. The links were made of heavy wire, had a loop at each end,
and were joined together by three rings. The outside ends of the handles fastened to the end
links were the 0 and 66 feet mark. Successive tags had one, two, three or four teeth to mark
every tenth link from each end. The center tag was round. With 600 or 800 connecting link
and ring surfaces subject to frictional wear, hard use elongated the chain, and its length had to
be adjusted by means of bolts in the handles.
Figure 5A-2
Gunter's chain.
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Distances measured with chains were recorded either in chains and links or in chains and
decimals of chains, for example, 7 ch 94.5 lk or 7.945 ch. Decimal parts of links were
estimated. The 66 feet length of the Gunter's chain was selected because of its relevance to
the mile and the relationship of a square chain to an acre. Thus, 1 ch = 1/80 mile, and 10 ch ²
= 10 x 66² = 43,560 ft² = 1 acre. An engineer's chain had the same construction as a Gunter's
chain, but was 100 feet long and each of its 100 links had a length of 1 foot. Tapes are made
of steel 1/4 in to 3/8 in wide and weigh 2 to 3 lb/100 ft. To use a tape the rear tape person
holds the 100 ft end of the tape over the first (rear) point, while the forward tape person,
holding the zero end is lined in over the next point. For accurate results, the tape must be
straight and the two ends held at the same elevation. A specified tension, generally 25 lbs., is
applied. To maintain a steady pull, tape persons wrap the leather thong at the tape's end
around one hand, keeping forearms against their bodies, and faced at right angles to the line.
In this position, they are off the line of sight. Sustaining a constant tension with outstretched
arms is difficult for a pull of 25 lbs. Also, steel tapes are standardized at 68 F (20 C). A
temperature higher or lower than this value causes a change in length. Weeds, brush, rocks,
etc. make it undesirable to lay a tape on the ground. Instead, the tape is held above ground in
a horizontal position. Each end point on the tape is marked by placing the plumb-bob string
over the proper tape graduation and securing it with one thumb. The rear tape person
continues to hold a plumb-bob over the fixed point, while the forward tape person marks the
length. When the tape has been lined in properly, tension has been applied, and the rear tape
person is over the point, the forward tape person then places a pin exactly opposite the zero
mark. They then proceed to measure each 100-ft increment until they reach a partial tape
length. In measuring the last partial tape length of a line a full foot graduation is held by the
rear tape person at the last pin set. The head tape person reads the additional length beyond
the zero mark. See Figure 5A-3.
Figure 5A-3
Partial length.
iron pin

33

4
3

2

1

0

 .75 
Thus, the last measurement is 33 feet and 0.75 ft.
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In measuring the distance between two points on a steep slope, rather than break tape every
few feet, it may be desirable to tape along the slope and compute the horizontal component.
This requires measurements also of either the angle of inclination  or the difference in
elevation d. Breaking tape is more time consuming and generally less accurate due to the
accumulation of random errors from marking tape ends and keeping the tape level and
aligned for many short sections.
5A.4.4 Electronic Distance Measurement
A major advance in surveying instrumentation occurred approximately 40 years ago with the
development of electronic distance measuring (EDM) instruments. These devices determine
lengths by indirectly measuring the time it takes electromagnetic energy of known velocity to
travel from one end of a line to the other and return. This indirect time measurement scheme
consists in determining how many cycles of electromagnetic energy are required to travel the
double path distance. The frequency (time required for each cycle) is precisely controlled by
the EDM instrument and thus known, so the total time becomes known. Multiplying total
time by velocity, and dividing by 2, yields the unknown distance.
The current generation of EDM instruments have combined with digital theodolites and
microprocessors. These devices called total station instruments can measure simultaneously
and automatically both distances and angles.
The most common system for classifying EDM instruments is by the type of electromagnetic
energy they transmit. Two categories are commonly employed in surveying: (1) electrooptical instruments, which transmit either laser or infrared light and (2) microwave
equipment, which transmits invisible electromagnetic energy of a very short wavelength.
In addition to their unique types of transmitted energy, other basic differences exist between
instruments in these two categories. A major difference, for example, is that signals
transmitted by electro-optical instruments are returned from the opposite end of the line by a
passive prism reflector.
Microwave systems, on the other hand, employ two identical units. One transmits the signal
to the other located at the opposite end of the line. The second unit receives the signal and
transmits it back to the original instrument.
The procedure of measuring a distance electronically is depicted in Figure 5A-4, where an
EDM device has been centered over station A by means of a plumb-bob or optical plummet.
The instrument transmits a carrier signal of electromagnetic energy to station B. The signal is
returned from B to the receiver, so its travel path is double the slope distance AB.
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Figure 5A-4
In the figure the modulated electromagnetic energy is represented by a series of sine waves,
each having wavelength. The unit at A determines the number of wavelengths in the double
path, multiplies by the wavelength in feet or meters, and divides by 2 to obtain distance AB.
The majority of EDM instruments manufactured today are electro-optical and transmit
infrared light as a carrier signal. This is primarily because its intensity can be modulated
directly, considerably simplifying the equipment.
5A.4.5 Surveying Instruments
Transits, theodolites, and especially total stations are perhaps the most widely used surveying
instruments today. The transit and theodolite are fundamentally equivalent and can
accomplish basically the same tasks. Their most important application is measuring
horizontal and vertical angles, but they can also be used to obtain horizontal distances and
determine elevations of points by stadia.
Total station instruments incorporate an electronic, or digital, theodolite, an electronic
distance measuring (EDM) instrument, and a microprocessor in the same unit. Thus, they
can accomplish all of the tasks of transits and theodolites, and in addition they can also
measure distances accurately. Furthermore, they can make computations with these
measurements and display the results in real time.
The transit was the first of these instruments manufactured. The first American transit was
produced by William Young in 1831. They were used until theodolites were invented. From
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the 1960's through the 1980's, theodolites were purchased by surveyors more frequently. In
the 1990's, total station instruments, with their automatic angle and distance readout
capabilities, became the surveyor's choice of instruments.
5A.5 Metes and Bounds Surveying
During America's first years, settlers came, squatted, and marked off boundaries of a parcel
by referring to a particular brook, a line of trees, or a ridge. The deeds of these parcels were
made up accordingly by trying to describe these boundaries. Anyone looking at a map of
land in a metes and bounds State will see this haphazard arrangement of parcels. The
immediate area of settlement is in general a mishmash of lines, whereas recent growth may
show a more orderly plan. When towns did attempt an orderly plan, swamps, mountains, and
rivers had to be circumvented, resulting in roads that meandered and spawning irregular
parcels of land.
Early deed descriptions were general rather than accurate. A person selling a parcel of a lot
might write the deed as "200 feet by 200 feet by the stone wall". If dimensions were not
known, it was easy to say that the lot ran "by the land of Jones; thence by land of Smith," and
so on. Land values and the number of private landowners was such that there was little or no
attempt to be specific.
With the end of World War II and the financial boom that followed, there would be a need
for new homes and more private ownership. Prices on land began to rise and so was the need
to accurately survey and map land ownership.
Deeds that read "by land of Jones; thence by land of Smith" were causing problems. While
the original owner of the parcel was alive he knew where his boundaries were, but his widow
or children may not have known the boundaries. Compounding that problem was the fact
that the "true" acreage wasn't really known. For instance, the owner might pace off the back
forty and tell the purchaser he was selling him forty acres; and so the deed would say "forty
acres plus or minus". Land has found to be "plus" for sale purposes and "minus" for tax
assessment purposes.
Other problems result when "plus or minus" property is subsequently divided and sold.
A purchase of a twenty-acre parcel, plus or minus, may or may not involve an actual twenty
acres.
The first thing a surveyor will do before surveying property is assemble data. Researching a
parcel of land normally commences when the initial contact is made between the land
surveyor and client. They "walk the lines" (boundaries) of the parcel as described, giving the
surveyor the client's "interpretation" of the parcel itself. Any corner monuments that are in
place can be flagged with ribbon, and any missing corners can be temporarily flagged; the
surveyor's notebook should record this information. Other notations, such as boulders,
barbed wire fences, trees of large size in a line with smaller growth on each side (indicating a
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line, especially if some barbed wire can be found protruding from the trees) are also recorded
in the notebook. Abutters to the client’s property are noted. Sometimes the surveyor will
contact them because they may provide information, a deed which may never have been filed
at the register of deeds office, or they may have a survey of their own parcel.
Once the surveyor has the sketch, as well as copies of any deeds or surveys found during the
field inspection, he then goes to the register of deeds office to study all deeds relating to the
parcel under investigation, as well as all deeds pertaining to abutting parcels.
With the background information, the surveyor is now ready to return to the parcel of land
and make his measurements.
5A.6 Corner Markers
Figure 5-5 shows the many kinds of corner markers, and there are many other kinds that are
used from time to time; pipes, wooden stakes, trees and even piles of stones.
Figure 5A-5
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5A.7 Order of importance
The hardest part of a mapper’s job and the responsibility of a surveyor is to determine the
intent of a deed when there are conflicting elements. The following outline of one order of
importance of conflicting deed elements, which is often quoted, has many exceptions, and
these are noted below.
Order of importance of conflicting elements that determine land location:
A
B
C
Right of possession (unwritten conveyance)
Senior right (in the event of an overlap)
Written intentions of parties

Call for a survey or an actual survey upon which the conveyance is based

Call for monuments
Natural or fixed, such as a watercourse
Artificial or manmade, such as a stake, iron pipe, or concrete marker

Direction and distance

Direction or distance

Area (quantity)

Coordinates
Senior rights may or may not be apparent from the wording of a conveyance. The importance
of all other items within a conveyance must be interpreted in light of the intentions of the
parties as of the time of the conveyance.
The order of importance of conflicting deed elements as listed above, while generally true,
can vary from state to state, and within the same jurisdiction it can vary under different
circumstances. In most states distance and direction are both subordinate to monuments or
adjoiner, but when it becomes necessary to choose whether direction or distance is
controlling consideration, variable and conflicting court opinions exist.
The following terms are frequently seen in deeds and plats to identify the status of a corner.

A corner is a point of change of direction of the boundary of real property. It may be
marked by a monument, fence, or other physical object, or it may not be marked at all.
A call for a point is assumed to be a call for a corner, but the call for a course without
the call for a point is not necessarily assumed to be a call for a corner.

An existent corner is one whose position can be identified (a) by an existing
original monument or (b) by acceptable accessories to the original monument
position.

An obliterated corner is one at whose point there are no remaining traces of the
original monument, replacement monument, but whose location may be recovered (a)
by competent testimony, (b) by some acceptable record of evidence, or by a
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monument proven to be a replacement of an original monument.

A lost corner is a point of a survey whose position cannot be determined by the
original monument or by acceptable evidence as to where the original monument
was.
Monuments called for in a deed, either directly or by a survey, or by reference to a plat which
the parties relied on, are subordinate to senior rights, clearly stated contrary intentions, and
original lines actually marked and surveyed, but are presumed superior to direction, distance,
or area. The surveyor must determine if the monuments called for in the deed were in place
at the time of the deed. Whenever an original survey is made, the surveyor either finds a
monument in place or sets a monument. The distance and direction measured between the
monuments is dependent upon the skill and accuracy of the surveyor doing the measuring,
and, if errors occurs, the error is due to the inability of humans to measure properly. The
monuments are fixed in position and, if found, undisturbed, are not in error. In deeds written
without benefit of survey and including calls for monuments, the presumption is that the
parties intended to go to the monuments, otherwise the calls would not have been inserted.
Because an original monument is considered as more certain in fixing the location of a line or
corner, it is given preference over distance, direction, or area. An uncalled for monument
cannot be considered controlling when in conflict with superior elements. For a monument
itself to be controlling it must be (1) called for, (2) identifiable, and (3) undisturbed. If the
monument is obliterated, it is controlling if its former position can be identified (a) by
reliable witness evidence, (b) by surveyor's notes, (c) by improvements.
Superiority of monuments over distance, direction, and area is so frequently accepted that the
danger of applying the principle comes from a contrary intent. If numerous other inferior
terms in a deed refute the call for a monument, and if the other terms taken together indicate a
contrary intent, the reason by which monument control is jeopardized.
5A.8 Senior Rights
Where two parties are given title to the same parcel of land, and where possession is not a
consideration, the party with the senior rights has the right of possession according to
common law.
Denna Banks purchased land from Karen Rathbone on 3/16/98 and her title reads, "The
westerly 50 feet of Lot A." Susan Gregory purchased land from Karen Rathbone on 3/17/98
and her deed reads, "The easterly 50 feet of Lot A." Because of the earlier time, Denna
Banks is said to be senior and she receives all of the land coming to her, as shown in Figure
3-6. Susan Gregory could not buy more than Karen Rathbone's remainder and is junior in
character. The overlap in Figure 5-6 in title belongs to Banks and if there is no possession
Banks has the right of possession. If, however, Gregory had possession up to her title line for
a prolonged period of time as required by law, her possession might give her the right to go to
court and obtain title to the overlap.
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Whether senior rights are investigated by the surveyor or not depends upon the custom within
the state and the terms of the contract under which he is working. In many states, especially
in the West, title companies issue title policies with senior considerations stated in the
description furnished. In such states it is advisable for surveyors to work with title policies
and deeds. In some states little or no title information is available and it is extremely difficult
to trace senior rights.
Figure 5A-6
Senior rights and overlaps.
5A.9 Call for an Adjoiner
A call for an adjoiner (bounded by Monteith on the east; to the line of Berry as described in
Book 1021, page, etc.) may be a call for a senior right, but not always. For example, Jimmy
Cox’s deed reads in part: “Bounded on the south by the land of Dan Stewart as described in
Deed Book 1918 Page 42, etc.” Dan Stewart’s deed reads in part: “thence N 0 27' 00" E,
301.27 feet to the southerly line of Jimmy Cox’s land as described in...etc.” Each calls for
the other. In such an event an extensive title search is necessary to determine who has prior
rights. They do exist! The cause of such ambiguity is usually a subsequent change of the
words or the form of a description after the first conveyance. Later owners cannot obtain
more than was described in the original document, except by the process of lawful prolonged
possession which ripens into a title right. The principle here is that a call for an adjoiner is
not always a correct criterion for determining senior rights. A title search back to the original
formation of the conveyance is necessary for a correct solution.
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5A.10 Principle of “Intent”
Various court rulings have helped define the principle of intent and guide a mapper as to the
proper location of a boundary line. Three of those rulings are as follows:
1.
The primary and fundamental principle to which all others relate and must yield is
that the intentions of the parties gathered from the whole instrument, taken in
connection with the surrounding circumstances, must control.
2.
A deed should be construed according to the intentions of the parties, as manifested
by the whole instrument.
3.
Principles given to determine the order of importance of conflicting elements are
not conclusive but are principles of evidence or principles of construction adaptable
to surrounding circumstances. A call that would defeat the parties intentions is
rejected regardless of its comparative dignity.
The following principles of construction, given to determine the control between conflicting
elements within a deed, are rebuttable presumptions subordinate to the preceding principle.
Like all principles based upon rebuttable presumptions, when the contrary is shown, the
presumption is overcome and the principle does not apply. In court cases involving land
boundary disputes the written intentions of the parties who were a part of the original
transaction are the paramount considerations; the written intentions control all other points.
When land is first conveyed, the transfer cannot be by parol means; in other words, evidence
gathered by testimony of witnesses; only a properly written and signed document in
accordance with the laws of the state can be used. To determine the intent of an instrument
from the parties of the transaction by oral statements is tantamount to permitting transfer of
titles by parol means. This is a violation of the statute of frauds. The intent must be
determined from the written instrument itself, not from the mistaken ideas of one of the
parties. Where a party believes he has a right to a disputed parcel of land and that right is not
based upon a written deed, only a court or a true title owner can transfer paper title. In such
cases, the mapper should advise the client to seek legal advice.
If two elements in a deed are in conflict, before a proper location can be made, it becomes
necessary to decide which one was intended and which one was informational. A deed
written “N 20 E a distance of 310 feet to Yelton Creek” presents a conflict because Yelton
Creek is 410 feet away. What was intended? Here the court rule is that the natural
monument, the creek, more clearly shows the intent than does the informative term “310
feet.” An additional problem is whether the line goes to the sideline of the creek or to the
thread or center of the creek. In this case it would be improper to ask the buyer or seller what
the intentions were; the document as signed is the best evidence of intent. In most states, if
the stream is navigable, the line stops at the side of the creek; if it is not navigable, the line
stops at the thread or center of the creek.
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As early as 1858 it was stated, “The rules adopted in the construction of boundaries are those
which will best enable the courts to ascertain the intentions of the parties. Preference is given
to monuments, because they are least liable to mistake; and the degree of importance given to
natural or artificial monuments, course and distances, is just in proportion to the liability of
the parties to err in reference to them. But they do not occupy an inflexible position in
regards to each other. It may sometimes happen, in case of a clear mistake, that an inferior
means of location will control a higher.”
The intentions of the parties to the deed must be gathered from all the terms of the deed, each
term taken in the light of all other terms. A call for a monument, though normally
controlling, may be rejected where all the other terms in the deed indicate that the call for the
monument was inserted in error.
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Topographic Surveys – Introduction
Topographic surveys are made to determine the configuration (relief) of the earth’s surface
and to locate natural and culture features on it. From the survey data, using various types of
lines and conventional symbols, topographic maps that depict these resentations of portions
of the earth’s surface. Natural features normally shown on them include relief (hills, valleys,
and other surface irregularities), hydrography (rivers, lakes, oceans, etc.) and vegetation.
Cultural (artificial) features are the products of people, and include roads, railroads, and
buildings. Names and legends on maps identify the features.
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Topographic maps are made and used by engineers and planners to determine the most
desirable and economical locations of highways and railroads; by architects in housing and
landscape design.
A planimetric map depicts only natural and cultural features in their plan positions and does
not show relief.
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Objects shown in plan view are called planimetric features. Digital elevation models (DEMs)
and three-dimensional perspective models are newer methods for depicting relief, made
possible by computers.
5A.11.1 Methods for Topographic Surveying
Topographic surveys are conducted by either aerial (photogrammetric) or ground (field)
methods, and are often a combination of both. Refined equipment and procedures available
today have made photogrammetry accurate and economical. Hence, almost all-topographic
mapping projects covering large area now employ this method. Ground surveys are still
frequently used, however, especially for preparing large-scale maps of small area. Even
when photogrammetry is utilized, ground surveys are necessary to establish control and to
field-check mapped features for accuracy.
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5A.11.2 Control for Topographic Surveys
The first requirement of any topographic survey is good control, whether the survey is done
by ground or aerial methods.
Horizontal control for a topographic survey is provided by two or more points on the ground,
permanently or semipermanently monumented, and precisely fixed in position horizontally by
distance and direction, or coordinates. It is the basis for map scale and locating topographic
features. Horizontal control is usually established by traversing, triangulation, and satellite
methods, and can be filled in photogrammetrically for large areas.
Until recently, triangulation and trilateration were the most economical procedures to
establish basic control for surveys extending over large areas such as a state or the entire
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United States. These techniques are now giving way to satellite surveying systems.
Monuments of the state plane coordinate systems, having been established by control
surveys, are used to initiate surveys of all types, but unfortunately more are needed in most
areas.
Vertical control is provided by benchmarks in or near the tract to be surveyed, and becomes
the foundation for correctly portraying relief on a map. A vertical control net is usually
established by lines of levels starting from and closing on benchmarks. Elevations are
generally determined for all travel hubs.
Topographic details are usually built on a framework of control points whose positions and
elevations have been established.
5A.11.3 Contours
As stated earlier, contours are most often used by surveyors and engineers to depict relief.
The reason is that they provide an accurate quanitiative representation of the terrain. Because
planimetric features and contours are located simultaneously in most field topographic
surveys, it is important to understand them and their characteristics before discussing the
various field procedures used to position them.
A contour is a line connecting points of equal elevation. The shoreline of a lake is a visible
contour, but in general, contours cannot be seen in nature. On maps contours represent the
planimetric locations of the traces of level surfaces of different elevations. Contours are
drawn by interpolating between points whose positions and elevations have been measured
and plotted.
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The vertical distance between level surfaces forming the contours is called the contour
interval. For topographic quadrangles at 1:24,000 scale, the US Geological Survey uses one
of the following contour intervals: 5, 10, 20, 40, or 80 ft. Contour intervals of 1, 2, or 5 ft are
commonly used on large-scale maps for engineering design.
The contour interval selected depends on a map’s purpose and scale, and the diversity of
relief in the area. Reducing the interval requires more costly and precise fieldwork. In
regions where both flat coastal areas and mountainous terrain are included in a map,
supplementary contours at one-half or one-fourth the basic interval are often drawn.
Spot elevations are given for critical points such as peaks, sags, streams, and highway
crossings. Topographic mapping convention calls for drawing only those contours that are
evenly divisible by the contour interval. Thus for the 10-ft contour interval of the map,
contours such as 1100, 1110, 1120, and 1130 are shown. Elevations are shown in breaks in
the contour lines, and to avoid confusion, at least every fifth contour is labeled. To aid in
reading topographic maps, every fifth contour (each that is evenly divisible by five times the
contour interval) is drawn using a heavier line. Thus the 1100, 1150, 1200, etc. contours are
drawn more heavily.
5A.11.4 Characteristics of Contours
Although each contour line in nature has a unique shape, all contours adhere to a set of
general characteristics. Important ones, fundamental to their proper field location and correct
plotting, are listed.
1.
2.
3.
4.
5.
6.
7.
8.
Contour lines must close on themselves, either on or off a map. They cannot
dead-end.
Contours are perpendicular to the direction of maximum slope.
The slope between adjacent contour lines is assumed to be uniform. (Thus it
is necessary that breaks in grade be located in topographic surveys.)
The distance between contours indicates the steepness of a slope. Wide
separation denotes gentle slopes; close spacing; steep slopes; even and parallel
spacing, uniform slope.
Irregular contours signify rough, rugged country. Smooth lines imply gradual
slopes and changes.
Concentric closed contours that increase in elevation represent hills.
Contours of different elevations never meet except on a vertical surface such
as a wall, cliff, or natural bridge.
A contour cannot branch or wye into contours of the same elevation.
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Section 5A
Review Questions
1.
The two classifications of surveys utilized primarily by cadastral mappers are
___________________ and ______________ surveying.
2.
_______________ surveys are run for the purpose of relocating or
reestablishing previously surveyed boundary lines.
3.
EDM’s measure distance by the amount of time it takes
energy to travel from one point to another and return.
4.
The order of importance of conflicting elements are:
________________________, ______________________, and
___________________________________.
5.
For a monument itself to be controlling it must be _________________,
_________________, and _________________________.
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Solutions
Section 5A
Review Questions
1.
The two classifications of surveys utilized primarily by cadastral mappers are
GEODETIC and PLANE surveying.
2.
RETRACEMENT surveys are run for the purpose of relocating or
reestablishing previously surveyed boundary lines.
3.
EDM’s measure distance by the amount of time it takes ELECTROMAGNETIC
energy to travel from one point to another and return.
4.
The order of importance of conflicting elements are:
RIGHT OF POSSESSION, SENIOR RIGHT, and WRITTEN INTENTIONS.
5.
For a monument itself to be controlling it must be CALLED FOR,
IDENTIFIABLE, and UNDISTURBED.
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