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 Cadastral Surveys
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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:

  • demarcation on the ground of the boundaries of the rights; and

  • Legally authorized document depicting the location of the boundaries.

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 solutions to almost all their needs.

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