## 4 Discussion  
In the article, we introduced the method of joint georeferencing of a multi-sheet map work with the conditions of continuity of the adjacent edges of map sheets. It can be used where the parameters of the used cartographic projection are not known. The methods of georeferencing old maps using simple geometric transformations and the adjustment using LSM are generally known and used. Alternatively, interpolation algorithms for rubber-sheeting methods are applied. Examples of georeferencing single-sheet early maps can be found in [30; 31]. In our case, we work with multi-sheet map works, which is significantly more complicated. Mathematically, it is possible to use the conditions of a sheet continuity during the adjustment [5; 6], georeferencing the entire mosaic merged in the original coordinate system [1; 4], or use a local transformation method based on, e.g., grid shift binary (GSB) as a second step [9]. For the georeferencing of the First Military Survey, the Arcanum project used the method of georeferencing the whole mosaic of each province using 30-50 GCPs and a polynomial transformation in as early as 2011 [32]. The accuracy of such georeferencing was not great. This method was later supplemented by a local type of transformation. The transformation of the whole mosaic using the local GSB method after adjusting the parameters of the estimated [PERSON]'s projection was also used for georeferencing Moldavia and Walachia [33]. The accuracy of local methods reaches average deviations on GCPs of around 200 m. Roughly corresponding accuracy is achieved by our method, which, however, does not use [PERSON]'s projection and GSB, but only a polynomial transformation with the conditions of the continuity of map sheets. Therefore, the comparison of the accuracy of both approaches on a set of checkpoints will be described below. A group of 50 control GCPs that did not match the points originally used for the global adjustment was used to assess accuracy. As presented above, the results do not clearly show that one of the methods would be significantly geometrically more accurate, or rather the set of GCPs used is not able to prove this. The data show the predominance of smaller deviations (sometimes in the order of meters or tens of meters, i.e., well below the total mean square error value) in the case of Mapire.eu, but they are balanced by relatively large positional differences, in some cases exceeding 1 km (which practically represents a borderline value for IRLS) and extending up to 2 km. This coincides with the visual observation where some parts of Bohemia show significant positional differences and are strongly deformed. When looking at adjusted map sheets using IRLS, it is clear that substantial deformations of the sheets, except for several peripheral positions, practically do not occur. Certainly, within the research a large amount of GCPs was collected and the used mathematical method is more complex than the GSB method available in common GIS software. Anyway, the results of our adjustment are more resistant to gross errors and the deformation of the map sheets after the transformation is not as noticeable. Additionally, the transformation outside the convex hull of GCPs is much better using polynomial (or affine) transformation than using interpolation based on GSB. That is why we considered our approach to be beneficial. The medians of positional deviations are practically the same in both cases, which may indicate a similar explanatory value of both approaches and different errors at individual points due to random fluctuations of both methods rather than due to a systemically defective approach of some of them. Multiple GCPs would be needed to make a good assessment of the method used on Mapire.eu, which will be done in further research. The difficulty of this approach is a considerable exhaustion of some sites in terms of identifiable points where their compliance can be guaranteed.