MultiMap. This means that the geometrical accuracy 
should lie in 25 - 30 meters in ICNW and 5 -10 meters in 
metropolitan areas. 
The data capture is carried out manually (Fig. 2.1). Analog 
maps or orthoimages are scanned first. These digital raster 
data should be transformed in the MultiMap reference 
system and converted into the specified digitization image 
format, before they can be displayed on computer screens 
and then digitized. Available vector data can also be 
integrated into the digitization process, so that data 
capture can be speeded up. 
On the basis of these data plots are generated for field 
data collection (FDC). Taking these plots with them, the 
field surveyors make site-the-spot investigations to collect 
necessary traffic-relevant attributes and to mark possible 
errors.The collected data are then put into the data base 
manually. 
Differential GPS is used as a supplement measure for 
areas where available source materials are out of date or 
no up-to-date ones are available. 
An individual quality checking is catered for every step in 
this vectorization process. For data base release, a 
specially developed strict complex checking process is 
carried out. 
In order to ensure the high quality of MultiMap 
permanently, updating with high quality data should take 
place fast enough, before changes in reality occur again. 
Instead of collecting every piece of information ourself in a 
long costly process, relevant publishing houses, civil 
engineering offices, driving schools and taxi associations 
etc. are incorporated in order to obtain up-to-date high 
quality source data. Naturally it goes without saying that all 
of this information is verified, if necessary, on location by 
the FDC before it is added into the database. Using this 
process, we are able to release an updated database twice 
a year. 
2.3 Data capture through digital Photogrammetry 
In many cases digital orthoimages will be the best solution 
in terms of up-to-dateness, reality, accuracy and rich 
information, which are essentially vital for the MultiMap. A 
disadvantage compared to maps is that they don't carry 
notations like street names. Another shortcoming is that at 
the moment the costs of using Photogrammetry are 
relatively high. 
Digital and analog orthophotos have been successfully 
used in our projects Austria and Switzerland respectively. 
In Austria the department Land Topography of the 
Bundesamt für Eich- und Vermessungswesen (BEV) 
possesses different map works, which were suitable as 
source materials. For the street network outside cities the 
digital data from a BEV-database were used. This 
database is built with photogrammetric stereo-restitution 
method and currently further densified by the BEV. At that 
time only an ICNW was available in addition to objects like 
administrative boundaries, waters etc., so that further 
source materials were needed for data densification in 
metropolitan areas. For this purpose orthoimages (scale 
1:10.000) in analog form were bought from the BEV, which 
were then scanned in our production. 
It was more difficult to obtain source materials for 
Switzerland, since the Schweizerische Eidgenóssische 
Vermessungsdirektion (SEVD) conducts only small scale 
maps (1: 25 000 or smaller). The 1: 25 000 topographic 
maps were applied for acquisition of ICNW. The large scale 
maps (up to 1:10 000), needed for data densification in 
metropolitan areas, are conducted respectively by the 
individual federal states (Kantone). In order to keep source 
materials for the planned metropolitan areas to be 
homogeneous, digital black & white orthoimages (1 meter 
ground resolution were ordered with the company 
Swissair, which were rectified from latest photogrammetric 
flights. 
These digital orthoimages were then transformed from the 
respective national coordinate systems into the MultiMap- 
conform reference system and converted into the special 
image format suitable for the on-screen digitization, before 
they can be loaded into our digitization stations for the 
vectorization process in our production. 
The accuracy of orthoimages is usually strongly influenced 
by the used basic data like the quality of DEM. During the 
digitization cases were observed where the images didn't 
fulfil our accuracy requirements, so that additional sources 
(DGPS measurements, other map materials) were 
necessary. This problem was put down to the errors 
coming from the rectification processes. 
In the Austria project, the digitization was made difficult 
because of bad quality of several images. These images 
can be divided into 2 groups: the one with bad photographic 
quality (contrast, disruptive pixels) and the other negatively 
influenced by unfavorable flight time (dense leaves, 
unfavorable sun position). This problem was not 
encountered in the Switzerland project. 
With one meter resolution images, it was often very difficult 
to recognize some small details such as road markings and 
small streets. In future work resolutions of less than 0.5 
meter should be applied. 
Photogrammetric materials are currently solely applicable 
large scale sources in Austria and Switzerland, owing to the 
up-to-dateness and lack of other economical alternatives. 
The same situation occurs partly also with the acquisition of 
digital road data in the Scandinavian regions. 
In general, the orthoimages proved to be effective in both 
projects. In order to improve our future working process, 
following points should be investigated: 
- improve data exchange in digital form to avoid using 
analog source materials. 
- install an improved method to increase photographic 
quality. 
- use color orthoimages for the digitization process. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996