ponding to a connected component. The arcs of the 
graphs correspond to the lines and are attributed with 
the thickness of each line segment. The nodes corres- 
pond to the line crossings and are attributed with the 
coordinates and the thickness of the line crossing. 
Examples for concepts are graph, node and arc as well 
as small graph and large graph. The nodes and arcs are 
parts of the graph. The small graph and the large graph 
are specialisations of the graph according to the special- 
isation condition that the area of the bounding rectangle 
of the graph as well as the ratio between this area and 
the sum of the length of the arcs are below or above the 
corresponding thresholds. 
The fourth level is called "image". It is the result of 
scanning the map and binarisation. This level consists of 
the two dimensional matrix of binary pixel values (raster 
image). The existing neighbourhood relations between 
the pixels are not used in our model. Operations on the 
image are image processing routines. They always pro- 
duce raster images as output. 
32. Relations and operations between the levels 
  
There are four different types of relations and opera- 
tions between levels. 
The first type connects the semantic objects level with 
the graphics and text level. It consists of the relations 
between the graphics and text objects on the one hand 
and the semantic objects on the other hand as given by 
the map legend. No operations are used. 
An example is the relation given by the map legend that 
boundary lines correspond to polygon 0.35mm, that 
topographic lines correspond to polygon 0.18mm and 
that boundary stones are symbolised by circle_1.9mm. 
The second type connects the graphics and text level 
with the image graph level. A relation between the size 
of a graph in the image graph and the type of objects 
(graphics or text) is used. Operations perform the trans- 
ition from arcs and nodes to graphics objects. 
The concept polygon for example is a specialisation of a 
concept arc that belongs to a large graph. The concept 
RO consists of all nodes and arcs that belong to a small 
graph. 
The third type connects the graphics and text level dir- 
ectly with the image level. Only operations are used. 
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They extract symbols, characters and digits from the 
binary image. In chapter 4.2. an example is given for the 
extraction of the concept circle 1.9mm by means of 
template matching. 
The fourth type connects the image graph level with the 
image level. Only one operation is used. It consists of line 
extraction from the image followed by a graph building 
process. An example of the application of this operation 
for the creation of instances of the concepts node and 
arc is given in chapter 5. 
4. FLOW OF THE INTERPRETATION 
The goal of our first test was to find the parcel areas, the 
general areas and the remaining objects in a Bavarian 
cadastral map of scale 1 : 1000. Therefore the flow of 
interpretation is only described for this example. The 
interpretation is restricted to parcel areas, because the 
corresponding numbers that are also parts of the parcels 
are not yet recognised. 
To achieve the goal we have to instantiate the concepts 
PA, GA and RO. For reasons of simplicity we make no 
difference between the concepts BS, TL and their sym- 
bolisation (circle 1.9mm, polygon 0.18mm). The con- 
cept BL consists of the parts polygon 0.35mm and BS. 
In the following the instantiation of the concepts is 
shown. The instances created from the concepts are the 
interpretation of the scene. 
4.1. Bottom-up instantiation of the concepts 
  
The instantiation of some of the concepts from the gra- 
phics and text level is a simple bottom-up process. The 
given instances of the nodes and arcs are analysed ac- 
cording to the type of the graph they belong to (lar- 
ge/small graph). 
If a concept arc belongs to a large graph, then an instance 
of the concept polygon is created. The thickness of the 
polygon is calculated as a mean of the thicknesses of the 
line segments of the arc. 
If concepts arc and node belong to one small graph, then 
an instance of the concept RO is created. All the related 
nodes and arcs are parts of the concept RO. 
The condition for the instantiation of the concept PA is 
that there exist instances ofthe concepts BL and BS. The