KARTOGRAFISCH TIJDSCHRIFT
2OOO-XXVI-4
Besluit
De iteratieve Procrustesanalyse is een probaat middel om kar-
teernauwkeurigheden te bepalen op de producten van histori
sche karteringen. Het is eveneens een wiskundig-statistische
methode om, naast andere historische methoden zoals de heu-
ristiek, na te gaan in hoeverre bepaalde kaarten gekopieerd
werden en in welke mate daarbij preciesheid werd nagestreefd.
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Summary
F. Depuydt J. Theelen - The metric accuracy of old maps.
Keywords: historic cartography, co-ordinate Systems, research
Thanks to the high-speed Computer processing of digitized points
on old maps and on the corresponding current map, it has become
possible, by means of the iterative Procrustes analysis method, to
express graphically and statistically the metric evaluation of the
historical mapping activities. The proper Procrustes method is a
similarity transformation and was employed here in an iterative
or repetitive way on Mercators map of Flanders and on the copy of
this by Ortelius. Just like the method invented by Mekenkamp,
the accuracy is graphically expressed by inaccuracy circles. Contra-
riously, the circle radius is here drawn proportionally to the real
mapping deviation on the historical document. The direction of
the radius correspond to the real displacement of the measured
point on the historical map.
The results unearths some interesting facts that lead to afew nota
ble conclusions:
The overall average deviation on Mercators map is about 813
meter; on Ortelius'copy it corresponds to 1,020 meter.
The difference between the two historical documents is on aver
age only 630 meter.
The central area of Mercators map is more accurate (an inac
curacy of 130 tili 300 meter) than the border areas ofthe Duchy
ofFlanders (an average of more than 1,000 meter).
The preference in the direction of deviations in certain regions is
caused by the accumulation and propagation of triangulation
errors made in the field.
This method can succesfully be used to examine the relationship
and the interdependency of two similar maps.
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