N K Agrawal
Managing Director, Geodesy and GPS Services,
Survey of land, preparation of cadastral maps and land records in paper and/or digital form, in a comprehensive land information/management systems, involves a number of processes. A number of difficulties/problems exist in the whole process. An attempt has been made to detail and discuss these and suggest possible solutions from a technical point of view
The first and foremost task is to survey the land which consists of data capture relating to individual land holdings, natural and man made features of land, boundaries etc. in their correct relative positions and to present these in the form of a map on a desired scale. The following steps should be considered:-
- Reference Surface/ Datum
- Projection / Grid System
- Method of Survey: control, photogrammetric, field data capture/ field and scale of survey
- Cartographic design/ mapping and digitization of documents
- Integration of data and creation of LIS/ GIS and Training
Reference Surface / Datum for India is Everest Spheroid which is a local system given by Sir George Everest who was Surveyor General of India from 1830 to 1843. All our cadastral survey maps are supposed to be on this datum. Cadastral survey maps of some of the states viz. TN, Kerala etc. refer to this datum whereas no datum is taken in respect of a number of states. Vertical datum for heights is however Indian mean sea level or Indian geoid which is supposed to be an equipotential surface of earths attraction and rotation. GPS however gives coordinates in WGS 84 system which is a global geocentric system. The two systems differ and the coordinates will have to be converted into Everest through transformation parameters. It is however of great importance that all cadastral surveys and mapping is done on one datum which is Everest Spheroid for India. All those states without any datum or surveying arbitrarily, will have to adopt the datum for uniformity and proper integration of surveys/data.
Mapping is carried out on a three dimensional earths surface / reference surface whereas maps are produced on a two dimensional plane surface. This is done through map projections. Some distortions in angles, distances, shapes or area take place which are taken into consideration for choice of a projection system. The projection system is also necessary for digitisation and computerisation of land records (COLR).
Some of the states e.g. TN, Andhra Pradesh etc. adopt a projection known as Cassini Projection. This projection is suitable for small areas i.e. nearly 60 to 70 kilometers on either side of central meridian. Each district therefore had a different origin thus having a number of coordinate systems in one state. It is therefore advisable to adopt Transverse mercator / UTM or Lambert conformal conic projection. These two projections are excellent projections used extensively all over the world and suitable for large areas covering any one full state of India. These are conformal (shapes are preserved) and have minimal scale distortion. It is therefore recommended that one of these two projections should be adopted by each state. There will be only one origin, one coordinate system and one type of seamless data for each state so as to have easy integration of data for LIS/ GIS. A regulation will be necessary that not only cadastral survey but all types of surveys to be carried out in that particular plane coordinate system of the state. A number grids have been designed for various states in Lambert conformal conic projection namely TN Grid, A. P. Grid, Karnataka Grid, Maharashtra Grid, Gujarat Grid.
Various cadastral survey conferences have deliberated on the projection to be used for Cadastral surveys. 12th All India Cadastral Survey Conference constituted a committee headed by Additional Surveyor General of SOI with some Directors, Land Records as members to standardize framework, projection, scale, contents, symbols and accuracies in respect of cadastral surveys and mapping. I am afraid , nothing has come out of the same. It is recommended that Transverse Mercator or Lambert Conformal Conic be adopted by various states depending upon whether their extent is N-S or E-W. It is not difficult to decide other matters e.g. framework, scale, accuracy, etc.
Methods of Survey
Conventional as well as Modern methods are being used. We will discuss modern methods only. Photogrammetric survey has been adopted by some states e.g. Madhya Pradesh and Orissa (Angul Nalco Project). It appears Andhra Pradesh is not happy with photogrammetric survey. Orissa has tried Angul Nalco in association with R&D Directorate of Survey of India.
GPS and Total Station: These are modern surveying tools, capable of producing surveys of required accuracy, economically, efficiently and speedily. GPS is a space based method whereas Total Station is a combination of EDM and Theodolite. Both are friendly to creation of LIS and GIS. GPS can be used as a Total Station also. GPS in relative mode should be used for providing main control up to village boundary. Total Stations can then be used for surveying land parcels and other details. This has been tried in Survey Training Institute during training of officer-trainees.Conventional instruments and methods can also be used in combination with modern methods in order to get best and economic results depending upon various situations and availability of instruments, manpower, and funds. One should first define the aim and plan to achieve the same with minimum expenditure of time and money.
Accuracy (Relative) of the present cadastral survey maps varies from 1:100 to 1:1000 at most which is insufficient. International standard for cadastral survey is from 1:20,000 to 1:100,000 . In India the main control for cadastral surveys should be 1:20,000; subsidiary control 1:10,000 and ordinary traverse control / survey with total station better than 1:1,000.
This will take care of surveys in towns also, where cost of land is very high. All corner points in towns should be established with accuracy of 1 to 5 cm. whereas in villages it could be up to 20 cm. State control, on which main control is based, should be of the order of 1:100,000. Instrumentation and methods of survey are based on the desired accuracy. It will greatly help if control in each state is provided with GPS or otherwise, as given below, with permanent monuments as control points:-
|50 km apart||1:100,000|
|20 km apart||1: 20,000|
|05 km apart||1: 10,000|
|02 km apart||1: 5,000|
Cartographic Design/Mapping and Digitisation of Documents
These are not being discussed here. Standard procedures are available. A technical committee can go in to these to standardize the procedures in respect of cadastral surveys / maps.
Integration of Data and Creation of LIS/GIS
Digitisation and then integration of data for LIS poses problems if the data is not seamless. We have various types of data e.g. with or without datum, projection system, accuracy, quality, standards etc. It will be a nightmare integrate the data, as the metadata (data about data) are not available . The following data about data should always be asked for :-
- Projection System
- Date of survey / Capture of data
- Accuracy of survey / data
- Parameters of datum and projection system
- Instruments used
- Adjustment procedure
- Method of collection of data
Requirements of cadastral survey for any one state is given below:
- Data in one datum
- Data in one projection system
- Seamless digital data
- Appropriate methodology
- Legal sanction with mandate to carry out all surveys as per above regulations
Creation of LIS or GIS will then not pose any difficulty
Lack of training is the greatest problem. We just go in to new technology and buy new instruments without proper preparation, planning , knowledge and training. It is therefore appropriate that manpower should be developed by proper training. Survey Training Institute of Survey of India can give training to Instructors, who in turn can give training to others in State Survey Training Institutes. Short courses in GPS and modern technology should also be attended by executives and administrators, who are decision makers, so that they may be able to take correct decisions.
We should adopt one grid / projection for each state, construct survey monuments 2 km. apart; provide control by GPS all over the state; create data bank; recruit and train the required manpower in phases; standardize and adopt survey / mapping procedures; enact legal laws if necessary and create LIS / GIS for better decision making and development.