Prof.
Stig Enemark
Aalborg University, Denmark
Fibigerstrede 11, DK 9220 Aalborg
E-mail: enemark@i4.auc.dk
ABSTRACT
The establishment of digital cadastral maps covering the total country of Denmark was completed by the end of 1997. The days of the old analogue cadastral processes are over. The new challenge will be to make this new digital product understandable and useful for a wide range of users. This may, however, not be a simple task. Even if the concept of the digital cadastral map is tailored for efficient interaction with other spatial information systems, there may be a number of problems to solve. These problems relate partly to the legal status of the cadastral map which may not be consistent with the topographic map, and partly to the problems of maintaining the digital cadastral map through a dynamic process of continuous improvement. A general understanding of these problems is essential for all users. In other words, the success of the digital cadastral map depends on the degree of the educated use of the map. These problems - and the Danish experience - will be addressed in this paper.
INTRODUCTION
The establishment of digital cadastral maps covering the total country was achieved by the end of 1997. The process commenced with a pilot-project carried through from 1985 to 89, and the continued computerisation of the maps then took place during the first eight years of the 1990īs.
The aim of this computerisation of the cadastral maps was to establish a digital cadastral information system which (i) would be tailored for efficient interaction with other spatial information systems; and (ii) provide an effective and secure process of land registration and land transfer.
The latter aim may easily be achieved since a simple scanning of the old analogue maps would provide an efficient digital process. The former aim, however, is the main reason for establishing a digital cadastral database. And this aim is not easy to achieve. This is due to the fact that the cadastral map has a special status as a "legal map" which - for many reasons - may not be consistent with the topographic map.
The demand for an absolute accuracy is rather small in this "legal map". The cadastral process is focused on the relative accuracy between the parcel boundaries. However, the users (local land use authorities, utilities etc.) will see the absolute accuracy as necessary in order to be able to combine the legal property features in the cadastral map with the spatial features in the large scale topographic maps.
The tension between the relative and absolute accuracy of the boundaries may therefore be seen as the main problem of establishing and running the digital cadastral map. The relative accuracy must be sustained for legal reasons while an absolute accuracy should be obtained for the reasons of multipurpose use.
This is why the procedures for updating the digital cadastral map will be opposite to the procedure for updating the analogue map. In the analogue map new boundaries were adjusted graphically to the position of existing mapped boundaries. In the digital cadastral map any new cadastral measurement will be used for adjusting the position of the existing boundaries. This will establish a process of continual improvement of the accuracy of the map - a dynamic system.
It is however recognised that some problems may arise in practice when a decision has to be made on the area to be included in the adjustment. A general understanding of these problems related to the process of establishing and maintaining the digital cadastral map are essential for all users. In other words, the success of the digital cadastral map will depend on the degree of educated use of the map.
These problems - and the Danish experience - will be addressed in this paper.
THE DANISH CADASTRAL SYSTEM
The Danish cadastre, which derived from the results of the enclosure movement, was established in the year 1844. From the beginning the cadastre consisted of two parts; the cadastral register and the cadastral maps. Both of these components have been updated continually ever since.
As a result of the enclosure movement, the former feudalistic society was changed into a society based on private ownership to land. The necessary maps were surveyed by plane table at a scale of 1:4,000. The resulting property framework from the enclosure movement formed the basis for the new cadastral maps. Each map normally includes a village and the associated cultivated areas. As a result the maps are "island maps" covering different areas and not based on any local or national control network.
The boundaries of the urban parcels in the villages were shown very approximately on the cadastral maps since these urban properties were not important for land valuation purposes. The provincial towns were surveyed separately based on a provision from 1863. The maps are established by traversed surveys, most of them in the scale of 1:800.
The parcels within each village area were numbered and recorded in the cadastral register showing parcel areas, parcel numbers , and the valuation of each property (being an aggregation of several parcels in the property) with the cadastral maps showing the location of the cadastral parcels. The present cadastral system is still based on these historic village areas which constitute the framework for the register and the cadastral maps.
Even if the primary purpose of the cadastre was to levy land taxes, the cadastral identification was also used to support the land ownership and land transfer system. Even though the cadastre was established in 1844, and it has been a requirement since 1810 that all subdivisions of land and all changes of boundaries had to be undertaken by private licensed surveyors. Simultaneously, in the year 1845, the Land Registry System was established by the local district courts for recording and protecting legal rights of ownership, mortgage, easements and leases for land.
The land registration system was established as follows:
Over time the Danish cadastre has changed from being primarily a basis for land valuation to a legal cadastre supporting an efficient land market as well as effective land use administration.
The process of cadastral surveys and land registration
When land is to be subdivided or property boundaries changed, both private and public landowners must apply by law to a private licensed surveyor for the necessary legal surveys and for the preparation of documents needed for submission of an application to the National Survey and Cadastre for updating the cadastre. The application must contain a copy of the cadastral map showing the alteration of the boundaries, measurement sheets showing the new boundaries, documentation for legal rights, as well as documentation showing the approval of the future land use according to planning regulations and land use laws.
The approval from the National Survey and Cadastre, showing the updated cadastral register and the updated cadastral map, is returned to the licensed surveyor. Simultaneously, the approval is forwarded to the municipality for updating of the property tax register, and to the local Land Registry Office for updating the Land Book. Deeds or mortgages may then be entered in to the Land Book based on the updated cadastral identification. The process of the cadastral work is controlled by the Subdivision and Land Registration Act which provides very detailed regulations.
To determine the existing boundaries the surveyor must compare the legal survey information (the cadastral map and the measurement sheets) with the real physical layout, placement of fences etc. If discrepancies are found the surveyor has to determine why. Maybe the land owners have agreed on another boundary without bothering to update the cadastre, or maybe the boundary in the field has been accepted by the landowner for more than 20 years which may lead to the establishment of a prescriptive right (a claim of adverse possession). In such cases, the licensed surveyor must involve the landowners. However, if the landowners cannot agree on the boundary, the licensed surveyor resolves the conflict through a special legal procedure for determining disputed boundaries.
Boundaries are surveyed to a high accuracy in a local sense and corners are typically marked with iron pipes. Today most surveys are connected to control points and linked into the national geodetic network (since 1934). Within a few years the demands for a fully digitised cadastral process will be mandatory.
The computerised cadastral system.
The cadastral register was computerised from 1984 to 1986 and the computerisation of the Land Book will be completed before the year 2000. The computerisation of the cadastral maps was completed by the end of 1997.
The basic function of the cadastral map will remain even after the maps are computerised. The benefits will be the multipurpose use of the maps, in combination with other land data registers and maps, leading towards cadastral based GIS-systems. The challenge was, to find the lowest acceptable standard for fulfilling these objectives in order to minimise the costs of computerisation.
This multipurpose use of the map requires in principle consistency with the topographic map. The demand for consistency refers to topographic maps at a scale of 1:1,000 in urban areas and 1:4,000 in rural areas. On the other hand, the historic legal identification of the boundaries must be kept intact even if the maps are computerised for multipurpose uses.
The old analogue cadastral maps are "island maps" which are not related to the national grid. Over time they have become distorted due to shrinkage, redrawing and updating procedures. Just digitising the analogue will not result in a multi-purpose map.
Recognising these problems, and accepting that the cost of computerisation of the cadastral maps must be reasonable, this computerisation process was undertaken in two stages:
The production of the digital cadastral map was controlled by the National Survey and Cadastre. About 80 per cent of the maps have been produced by the private surveying firms. This was done by the use of invited tenders and by issuing detailed guidelines to be followed in the production process. Some final control procedures was carried out by the National Survey and Cadastre.
Examples from digital the cadastral map are shown in Figure 1 and 2.
Figure 1. Example from the digital cadastral map - an urban area.
Figure 2. Example from the digital cadastral map - a rural area.
THE ACCURACY OF THE DIGITAL CADASTRAL MAP
By using the computerisation process presented above, the accuracy of the boundary coordinates may vary considerably, ranging from a few centimetres in some urban areas to several metres in some rural areas. Therefore, the digital cadastral map may not be consistent with a digital topographic map. However, it must be considered that the nature and origin of those two kinds of maps are fundamentally different.
Also, it must be noted that the digital cadastral map is a graphic map, not a numeric map. This means, that the coordinates for the boundary points only represent the boundary in the graphic map. The final determination of boundaries must be done according to the cadastral regulations. The parcel coordinates in the digital cadastral map therefore may not be used for exact calculation of parcel areas and dimensions.
The accuracy of the boundary points relates to the way these are established in the map. This information is therefore attached to the boundary point in the database. Boundary points established in the map using the control points and the cadastral measurements (forming the "skeleton map" as mentioned above) are indicated by circles. Information attached to the boundary points will indicate the method of establishment. Other boundary points which are inserted in the map using digitalisation of the analogue map are not indicated by circles but the attached information to all boundary features explain the kind of basic criteria used for establishing the boundaries in the map.
In this way, the accuracy of the boundary points can be estimated based on the attached information regarding the method of establishing the point in the map. The following accuracy’s can be expected:
The database will also include information on the kind of boundary (e.g. a boundary against road, railway, coast, lake or stream); information about administrative boarders (municipality, county, country); and information about the file number from the cadastral archives of the National Survey and Cadastre.
Finally it must be noted that some specific features in the cadastral map may not be consistent with the legal position of the boundary in the field. These features include:
These problems - as well as the problems of adverse possession - cannot be solved just by the process of digitising the map. Such problems can only be solved by the use of the detailed cadastral regulations for determining the legal position of the boundaries and the legal rights involved.
UNDERSTANDING THE DIGITAL CADASTRAL MAP
The concept used for computerisation of the old analogue cadastral map has resulted in a new issue with regard to the legal status of the digital cadastral map.
The Danish cadastral system was, so to speak, born with the cadastral maps established as a result of the enclosure movement in period 1780-1800. This original framework of boundaries has been maintained ever since. The legal basis for determining these old boundaries are not documented by cadastral surveys.
Since the early 1800īs it has been a requirement that all subdivisions and all changes of boundaries must be based on cadastral surveys sufficient for adjusting these new boundaries graphically to the position of the existing mapped boundaries. This means that the analogue cadastral map represented the only legal proof of the property boundaries, since there were no legal survey measurements determining the boundaries of the total property. The cadastral map therefore had to be used as the starting point for determination of existing boundaries when no legal survey measurements were available. This is still the case in many rural areas. In urban areas, however, most properties are measured to a high accuracy and documented by legal survey measurements.
The concept used for establishing the digital cadastral map has improved the absolute accuracy of the map to a high degree. And since the map is now based on the national grid network this improvement in accuracy will be a continuous process. However, in some areas this absolute accuracy may have been achieved at the cost of some relative accuracy.
The old analogue maps were not homogeneous due to the graphical updating process e.g. by fitting in major road infrastructures to the position of existing mapped boundaries. This may cause some difficulties for sustaining the relative graphical accuracy when converting the maps into digital form.
Furthermore, there is no guarantee that the identified elements in the topographic map used for transformation of the analogue maps actually represent the legal boundary point as originally established. These elements should, principally, be determined as boundary points in the field and coordinated to the desired accuracy. However, the procedure for establishing the digital cadastral map does not include these demands as this was estimated to be too expensive a process. Consequently, the basis for transformation of the analogue map is to some degree uncertain which may lead to uncertainty for sustaining the relative graphical accuracy.
In this way, it may be stated that the digital cadastral map has never assumed the legal status which was attached to the analogue map. The original relative accuracy is not present in the digital map. Where no legal surveys measurements are available, the determination of boundaries therefore has to be carried out on the basis of the old analogue map in force at the time when the boundary was established. The digital cadastral map may then be seen as a map presenting the registered land parcels in the best possible way (within fiscal limitations) to achieve the necessary format to facilitate multi-purpose use.
One may argue that the boundaries should just be presented consistent to the topographic map. This is not considered to be adequate since the cadastral system intends to maintain a registration of land parcels as a basis for and consistent with the legal rights of ownership and mortgage. For the same reasons a system of general boundaries is also considered to be inadequate.
The Danish cadastre has a long history and - as is the case in most countries - the system is closely connected to the cultural and legal context. This is why we will have to accept the problems connected to adapting the system to the concept of modern spatial information management. Also, this is why the success of the digital cadastral map will depend on the degree of educated use of the map.
MAINTAINING THE DIGITAL CADASTRAL MAP
The digital cadastral map is updated through daily routines in the National Survey and Cadastre based on the cadastral work for subdivision or change of boundaries submitted to the Agency by the private licensed surveyors. The process of updating includes an upgrading of the cadastral map with regard to the existing neighbouring boundaries. In the digital map any new cadastral measurements will be inserted directly in the map and they will be used for adjusting the position of the existing boundaries. This will establish a process of continual improvement of the accuracy of the map - a dynamic process.
This process of updating will also include a process of upgrading. Furthermore, this kind of upgrading may be carried out just for improving the cadastral map in specific areas and it may be carried out by the National Survey and Cadastre whenever suitable. This process of maintaining through upgrading may be seen as equivalent to the process of improving the analogue maps through redrawing.
The dynamic process for maintaining the digital cadastral map, however, results in some legal and technical problems which must be taken into consideration when carrying out the updating and upgrading process. The general problems of using the dynamic process is described in Figure 3, (Enemark, 1987).
The determination of boundaries as well as legal surveys for the purpose of updating the digital cadastral map are undertaken by the private licensed surveyors as a part of the cadastral work requested by the land owners. The private licensed surveyor may from 1st of January 1998 submit this material in a digital format and from 1st January 1999 this will be mandatory.
It is estimated by the National Survey and Cadastre that about 90 per cent of all updating can be carried out using the dynamic process without facing any problems. This is based on experiences from handling the updating process through the latest years. In the remaining 10 per cent, the dynamic process may result in some difficulties and require additional work. The amount of additional work then must be estimated in the actual case in relation to, for example, the number of land parcels involved.
There is of course a fiscal limit to be considered, and it may happen that the new boundaries just have to be adjusted to the existing boundaries without using the dynamic process. The private licensed surveyor may then contact the National Survey and Cadastre to investigate the possibilities of upgrading the map prior to carrying out the cadastral work. The National Survey and Cadastre may also decide that the upgrading should be postponed until a sufficient number of legal survey measurements within the area is submitted. An upgrading of the total area will then be carried out based on the new cadastral surveys.
Figure 3. Problems about using the dynamic process for updating the digital cadastral map.
Some general rules are established by the National Survey and Cadastre in order to control the process of dynamic updating:
Map-adjustment includes a simple graphical adjustment of the existing neighbouring boundaries. The changes should not be visible in the scale of 1:4,000 (e.g. straight boundary lines should still be seen as straight in the scale of 1.4,000). The length of the boundary should be at least twenty times the size of the adjustment of the boundary point (this is again to ensure that the adjustments are visible in the scale of 1:4,000).
Map-upgrading includes a transformation of the existing boundaries within a neighbouring area based on boundary reference points from the legal survey measurements. The choice of reference points must be considered by the licensed surveyor prior to undertaking the field work. Normally, the licensed surveyor will be well aware of the problems within his or hers normal district of work.
Map-adjustment and map-upgrading is not meant to take place for boundary points of high accuracy (boundary points indicated by a circle in the digital cadastral map).
The upgrading process will of course increase the accuracy of the cadastral map more than the process of adjustment and the graphical pattern in the map will be sustained by using map-upgrading (straight lines will still be straight etc.). Furthermore, the process of upgrading the map may be undertaken outside the normal process of updating the cadastral map in relation to new subdivisions or changes in boundaries. The upgrading process may be used just for the benefit of upgrading the map. This may take place e.g. prior to implementation of a major development scheme, prior to planning and expropriation for major road infrastructures, or a major land consolidation. Upgrading may also take place just for the benefit of improving consistency between the cadastral and the topographic map, e.g. for building up spatial information systems for specific purposes.
The processes for maintaining and improving the digital cadastral map are thus tailored for use in a modern GIS environment.
CONCLUSIONS
To establish a country wide digital cadastral map has been a major challenge to the National Survey and Cadastre as well as to the surveying profession. However, the real challenge will be to make this advanced product understandable and useful to a wide range of users: They should understand that the digital cadastral map in no way replaces or changes the legal boundaries; they should understand the nature of this map and the origin of the features; and they should appreciate that the digitalisation process was necessary to deliver a multipurpose cadastre for land administration and public access.
One way of doing it will be to introduce the product on the Internet and make it available just like any other kind of spatial information such as a road map. It is intended that the digital cadastral map should be available on the Internet in April 1998. Another way of doing it will be to educate the public about a number of applied uses of the digital cadastral map. In fact, this is already taking place. The era of the multipurpose cadastre is just around the corner.
REFERENCES
Enemark, S., 1987. Legal aspects by introducing a dynamic digital cadastral map in Denmark. OEEPE, Proceedings of the Workshop on Cadastral renovation, Lausanne, pp 21-32.
Enemark, S., 1994. Evaluation of the Cadastral Reform in Denmark - Training the Old Lady for the Skateboard. Proceedings of Commission 7, XX Congress of the International federation of Surveyors, Melbourne, 703.3/1-11.
The National Survey and Cadastre, Denmark, 1998. Det digitale matrikelkort - Ajourforingsvejledning (The digital cadastral map - updating guidelines). Only in Danish.
Williamson, I.P. and S. Enemark, 1996. Understanding Cadastral Maps. The Australian Surveyor, Vol. 41, No.1, pp 35-52.