compared to a line map. Both kind of maps are used in our forest administration depending on 
the general map situation. In the southern part of Rheinland-Pfalz, where large scale topographic 
maps exist, line maps are preferred while in the northern part of our state with only insular 
cadastral maps, they tend to use photo maps. 
Automatic drawing 
Regardless of this the forest administration lays down certain policies, rules and 
measures to be applied to timber production as fertilizing, pruning, production targets etc.. in 
thematic maps. So we were asked to produce automatically drawn maps to be used as forest base 
maps by digitizing the orthophotos containing the forest situation in combination with the property 
boundaries derived from cadastral maps. 
From a cartographic point of view forest maps are rather simple products. So to 
compete with manual methods we tried to keep the digitizing and the processing of the mapping 
data as simple as possible. 
For digitizing we use the Digimeter, an instrument measuring polar coordinates, 
manufactured by Coradi Switzerland. A keyboard allows to enter describing or controlling data. 
The output is on paper tape. Usually these instruments are employed in reallotment measuring 
areas. For data processing and automatic drawing we are equipped with a IBM 1800 and a high 
precision plotter Calcomp 745. 
In automatic drawing we have to do mainly with two kinds of files. The one contains the 
positions of the points or symbols and the other the information about the symbols and the 
connecting lines. In the automatic plotting of cadastral maps where we have to do with numbered 
and exactly defined boundary points we follow this procedure. We have a file of coordinates 
addressed by means of the point numbers and on the other hand a file of lines, where each line 
is defined by its two end points with their signatures. This latter file is gained automatically by 
splitting up the string of point numbers used for computing the areas of the lots. The application 
of a similar procedure to forest maps would be to expensive because we have neither sharply 
defined points nor numbers. Therefore we digitize in lines. A line is understood to be a string 
of points connected in the same manner without interruption. Each line is headed by a controlling 
record entered in the keyboard. This record contains information about the width of the line, 
whether it shall be drawn, dashed or dotted and about the signature of the points. It contains 
also the width of the roads. Small roads are hard to digitize with the necessary precision because 
the human eye is very sensitive to any deviation of parallelity ; therefore we measure only one 
side of the road. The other side is calculated as a parallel on ground of the width. 
Besides these line records there are special records whenever the position of the 
instrument has been changed on the draft to transform the measured polar coordinates into an 
orthogonal system. Another record at the beginning of the mapping data gives the scale of 
digitizing and the scale of the map to be plotted. 
The mapping data is processed without any storing. When reading the punched tape all 
processing is done simultaneously and the magnetic tape for plotter control in an off-line mode 
is written. ! 
A special problem in automatic plotting arises in the correction of errors and omissions 
in digitizing, especially in the addressing of the wrong elements. This difficulty may be overcome 
by introducing an interactive display into the process. Not having this possibility we chose another 
way. The lines are numbered automatically by the program in the order of entering and later on 
these numbers are printed in à preliminary plot. On account of these numbers stored in a table, 
wrong lines may be eliminated in a second run of the program by skipping these records when 
reading punched tape. The corrections are added like new measurements. 
It remains the problem with the knots. Knots are points where several lines intersect. 
The coordinates of the knots have been measured more than once, so differences may occur. By 
chosing a larger scale for digitizing than for drawing they may be kept within the accuracy of 
drawing. Otherwise they have to be corrected manually. This manual correction appears to us 
more convenient than a sophisticated adjustment of the knots, especially when dealing with such 
simple cartographic products as forest maps. 
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