441 
The accuracy s time-efficiency and reliability depend primarily on the 
precision of the measuring equipment and on the skill and care of the 
personnel involved. Thorough preparation is essential. Potential sources 
of errors and failures are the identification of control and tie points, 
especially on generalised maps, and separate measurements of differential 
heights and planimetry. In the latter case, mistakes in indexing or in 
the sequence of measurement are likely to occur (Radwan, 1980). Errors 
in DTM and in differential heights cause radial displacements which may 
be significant near photo-edges when terrain surface is rough (Beotra, 
1981; Besenicar, 1976). 
The updated information should be compatible with the existing graphical 
and the anticipated digital data base system(s). Compatibility concerns 
the data structures, formats and codes and the (added) relational data, 
i.e., to provide flexibility in manipulating and representing the basic 
data. 
CONCLUSION 
The recent achievements in the field of data base technology give reason 
to reconsider the existing techniques for updating maps. An up-to-date 
approach should serve two purposes, i.e., to update the existing map 
series and to contribute to a gradual transition from graphical to digital 
data bases. By accumulating the changes, adding new data items and rela 
tions and converting the existing data into digital format, a digital data 
base can be gradually built-up. 
It seems rational to anticipate that there will be an increasing transi 
tion from the original mapping to updating the existing data bases. The 
traditional economic and performance considerations about the alternatives 
of "updating” or "re-mapping" are no longer applicable to digital data 
bases. Correct "old" data should be preserved and supplemented by the 
"changed" and "added" new data, even if more than 50% of the total in 
formation has changed. Re-mapping is justified, however, if a higher 
accuracy is required. 
The operations typical for updating by DMP are involved in the preparation 
mensuration, and the geometric transformations. The properties of DMP in 
updating are listed below, separated according to technical and manage 
ment views. 
The technical properties are: 
- Control points and local DTM data can be extracted from existing topo 
graphic maps. Aerial triangulation and full DTM coverage are therefore 
not required; 
- Operation can be restricted to local zones of changes (except change 
identification and external orientation); 
- The transformation and correction algorithms are exchangeable, which 
provides versatility and flexibility; 
- The DMP output is suitable for updating graphical and digital data bases 
- The DMP software can be made compatible with other existing data base 
software systems; 
- The height of any point can be determined as a by-product. 
Some properties important for work management include: 
- The process is phased and thus operations can be parallel and decentra 
lised ; 
- Existing equipment can be used; 
- Each operation employs specific skills; 
- The control data, inclusive DTM, need not be available in the phases 
preceding the transformation stages.