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Cadastral
Surveys
Cadastral maps display the spatial descriptions of
land-parcel boundaries that define the location, shape and
size of land parcels within the context of a regional or
national geodetic positioning system. They also contain a
unique parcel identifier to establish the link to the
land-ownership information. When maintained in a real-time
manner, cadastral maps can serve as the base for a
reliable property rights system. Cadastral surveyors
established townships, lots, access roads, railways,
canals and town plots. Today, with global positioning
systems, surveyors are marking out new native land-claim
settlements and national parks to add to existing
provincial, territorial and international boundaries.
Digital images serve as excellent bases upon which
cadastral boundary data may be depicted. The combination
of digital images and cadastral boundary data provides a
powerful visual and management tool for a Land Information
System (LIS) or Geographic Information System
(GIS).
The LIS/GIS can be further enhanced with
descriptive records, such as legal ownership of land,
land assessments, property-tax records, boundary
descriptions, zoning, ground-cover information, civic
infrastructure, transportation networks and
communication routes. Some of these spatial information
themes may be directly extracted by digitizing over
image backgrounds.
Legal Surveys
A legal survey establishes official boundaries defining
the extent of a person's ownership, or other rights in
land. The word "land" includes renewable and
non-renewable resources, such as petroleum and mineral
resources, which are in or on the land. The survey
consists of two parts:
Cadastral surveys deal with one of the oldest and most
fundamental facets of human society-ownership of land.
They are the surveys that create, mark, define, retrace,
or reestablish the boundaries and subdivisions of the
public lands of any country.They are not like scientific
surveys of an informative character, which may be
amended due to the availability of additional
information or because of changes in conditions or
standards of accuracy. Although cadastral surveys employ
scientific methods and precise measurements, they are
based upon law and not upon science.
The recent "Statement on the Cadastre" approved
by the International Federation of Surveyors (FIG, 1995)
gives a generally accepted definition of the cadastre
and the relationship to the cadastral map as follows:
A cadastre is normally a parcel based, and
up-to-date land information system containing a record
of interests in land (e.g. rights, restrictions and
responsibilities). It usually includes a geometric
description of land parcels linked to other records
describing the nature of the interests, the ownership or
control of those interests, and often the value of the
parcel and its improvements.
The FIG Statement states that land parcels are defined
by formal or informal boundaries marking the extent of
lands held for exclusive use by individuals and specific
groups of individuals (e.g. families, corporations,
and community groups). Each parcel is given a unique
code or parcel identifier, such as an address, a
co-ordinate, or a lot number shown on a survey plan or
map.
Graphical indices of these parcels, known as cadastral
maps, show the relative location of all parcels in a
given region. Cadastral maps commonly range from scales
of 1:500 to 1:10,000. Large scale diagrams or
maps showing more precise parcel dimensions and features
(e.g. buildings, irrigation units, etc.) are
often prepared by cadastral surveys for each parcel
based on ground surveys and aerial photography.
Information in the textual or attribute files of the
cadastre, such as land value, ownership, or use, can be
accessed by these unique parcel codes shown on the
cadastral map, thus creating a complete cadastre.
Importantly, cadastral systems are not ends in
themselves. Their primary purpose today is to support
land tenure systems which protect land rights through
public recognition and recording, and support effective
land markets which allow land rights to be traded
efficiently and effectively. That is they permit land
rights to be bought, sold, mortgaged and leased. The
success of a cadastral system is a function of how well
it achieves these broad social and economic objectives,
neither the complexity of its legal framework nor the
technical sophistication of the cadastral surveys or
cadastral map.
Most parcel boundaries are defined by stable marks or
visible features on the ground, which can be natural or
artificial. They can be represented by lines on maps,
often described by bearings or azimuths and distances,
or by coordinates. If the representation on the map has
legal priority over the marks on the ground in cases of
dispute, the demands for survey accuracy are usually
higher than if the case is the opposite. Physical
demarcation on the ground is important because it
provides actual notice of the boundaries to the
landowners.
The demarcation and delineation of the boundaries are a
part of a cadastral survey aimed at defining the parcel
on the ground and securing evidence for the
re-establishment of the boundary if it disappears. As
the costs of cadastral surveys are relatively high, the
technical requirements of demarcation and delineation
(e.g. accuracy and survey methodology) should
reflect such factors as the value of the land, the risk
of land disputes and information needs of the users of
the Cadastre.
The basic spatial unit in a Cadastre is known as a
parcel. A parcel can be defined in many ways depending
on the purpose of the Cadastre. For instance, an area
with a particular type of land use may be considered a
parcel in some systems; in others it is defined as an
area exclusively controlled or owned by an individual or
group of individuals (e.g. family or corporation).
In some systems a property may consist of several
parcels of land which may be distributed over a small
region such as a village. The flexibility in the
definition makes it possible to adapt the cadastral
system to particular needs and thus also adapt the cost
of the registration. If, for instance, the purpose is
mainly to protect the ongoing traditional land use,
larger parcels representing common interests can be
defined as the basis for the system.
Cadastral surveying is usually undertaken using ground
survey methods. A cheap and simple method is to use
plane tables or tapes and optical squares. More
sophisticated methods include the use of electronic
distance measuring equipment or "Total Stations",
which usually give higher accuracies. Satellite
positioning fixing using the Global Positioning System
(GPS) is being introduced more and more and
promises to give high accuracy at a relatively low cost
in the future.
Cadastral surveying can also be undertaken by using
aerial photography. Today high accuracies can be
obtained using analytical photogrammetric methods. GPS
can also be used to reduce the costs of establishing
ground control. Other types of maps or images such as
orthophotos or enlarged photo prints can be used to
reduce costs in special areas, especially if a
systematic approach is used. Satellite images can today
only be used effectively in areas with very large
estates and open terrain and in scales smaller than
1:25,000, whereas most cadastral maps need to have
larger scales (1:500 to 1:10,000) depending on
the size of the parcels. Computerized mapping systems
and geographic information systems reduce the importance
of the physical map in favour of graphical data bases.
The latter are much more flexible for a multi-user,
multi-purpose environment.
It gives us great pleasure to provide world class
service in this field and it is our endeavour to remain
committed to our clients with economically viable
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