Geography Reference
In-Depth Information
the scale of the ancient map), such as the rotation angle with respect to the present
cartographic North, the scale variation throughout the map and the distortion of the
present cartographic grid as resulting after its adaption onto the old map. The process is
performed recognizing in the ancient map a proper number of still existing points, whose
cartographic coordinates can be derived from the present cartography. A specifically
designed software tool can result very useful for analysis of map deformations, allowing
the calculation of all the aforementioned parameters and their subsequent drafting in an
intuitive way (Jenny & Hurny, 2011).
The study of map deformation characterising the cartographic samples here analysed
showed scale factors quite variable throughout the maps, being slightly more
homogenous in F map than in P map. The average scale resulting from the calculation was
1:12,300 (1:14,300 ÷ 1:10,300) and 1:13,400 (1:16,600 ÷ 1:10,200) in F and P maps,
respectively. Notwithstanding this, the former map showed two severe anomalous
variation areas near the northern and southern delta lobe corners (Bitelli et al. 2009). In
particular, the northern gross deformation affecting F map is supposed to derive from a
shift of the drawing, intentionally made by the author for unclear reasons. L map
presented a bit more constrained scale factor (mean 1:11,200, range 1:13,200 ÷ 1:11,200)
and a smaller deformation than the other two, but it has to be taken into account that L
map depicts a smaller area in respect to F and P maps (Figure 4). Moreover, the calculated
rotation angles were 15.7°, 8.9° and 3.6° for F, P and L maps, respectively: they indicate an
angular displacement of about 7° between the first and the second map, and 12° between
the first and the third map.
In this specific case, where large areas, depicted in the maps, correspond to disappeared
coastal (i.e. peripheral) belts, points suitable to be used as GCPs cannot be found in the
present landscape, and the insertion of GCPs all around the deltaic area becomes obviously
impossible. The metric analysis that was possible to perform on the set of maps highlighted
gross deformations in all maps (especially in F and P maps). Notwithstanding some
differences in the results showed by the maps, this analysis alone resulted insufficient to
state which map has to be considered as the most faithful to the real asset of the ancient
landscape.
Thus, a question still remains open: why does exist a family of so severe deformations?
4. A second approach: a search for survey and draft step details
Due to their representation scale and their aims, the maps could be regarded as true
precursors of the modern “technical maps”. But it is likely that these wide-sized maps were
simply due to a scenic use of the products (e.g. for a good view during technical meetings
held in the presence of political authorities) rather than to a real technical need.
Unfortunately, up to now we possess neither the original field drafts nor the related field
notebook that could allow us to do an enormous quality jump in the detailed inspection of
the map generation process. Thus, any other analytical attempt must be taken into account
to try to find out information about survey and draft phases.
