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features are digitised - in continuous or stationary mode - and then 
transformed by means of DTM from the photo- to the model space, and 
further to the map (or field) coordinate system. 
The operations in updating correspond with those involved in data pre 
editing (i.e., verifying, correcting, completing and removing) of the 
original mapping. The term "updating" concerns changing the existing 
data items, addition of new items, and deletion of outdated data. These 
same operations are also involved in pre-editing, though updating is 
based on new data sources and the techniques may differ. 
Thematic mapping based on topographic or cadastral maps as geometric 
datum may be regarded (from a function viewpoint) as an updating process. 
The existing "datum" is supplemented with new data items. These, together 
with some items extracted from the existing "datum" form a dedicated 
(or thematic) data base. 
Because the scope of this paper is limited, not all facets of updating 
by digital techniques are dealt with. The emphasis is placed on the most 
pertinent technical issues. The overall process of updating, however, 
will first be outlined. 
OVERALL PROCESS 
General Considerations 
A data base system includes formation of the original data base and its 
subsequent manipulation. The DMP technique is applicable to both stages. 
In new mapping, the DTM grid is supposed to cover the entire region to 
be mapped, whereas in updating only local DTM data are needed, i.e., in 
the zones changed. 
In this paper, the term "changes" or "changed data" covers not only 
changes in the existing data items, but also addition of new items, and 
removal of the non-relevant data. The term "updating" applies to all 
changes. 
DMP for Updating 
The procedure for updating should reflect the type of the existing data 
base. Figure 3 shows, simplified, the alternative procedures for a 
graphical and a digital data base. 
Inputs 
I data files I 
Processes 
UPDATING 
BASIC DATA 
FILES 
GRAPHIC 
UPDATING 
I Updated |_ 
L .maps I 
Outputs 
digital 
graphical 
Fig. 3: Procedures for updating by DMP. 
The "basic data files" should contain correct, complete and consistent 
data - as specified for the original mapping. They form, together with 
the corresponding relations (e.g., links, topological), the core of a