## 2 Data and Methods
The first prototype of the software was written in Matlab, but it turned out that it would be better to use the possibilities of C++ for more demanding calculations. The software uses the Qt graphics library and works as a Windows application. It was also used for georeferencing Muller maps [29]. Another possibility to refine the results seems to be the introduction of weights into the calculation of adjustment. The weights should reflect different expected accuracy of individual types of GCPs (e.g., churches, yards, crossings, etc.) and their implementation requires additional knowledge of conditions in the area and especially the correct determination of weights based on experimentally determined a posteriori mean errors of individual adjusted coordinates. The scales then enter the adjustment as a diagonal matrix \(\mathbf{P}\), which contains inverse values of the mean square errors of the individual previously adjusted measurements. This can be done individually for all coordinates, but deriving weights only from a posteriori mean errors can be impacted with errors similarly to the measurements themselves. However, it is possible to use the categorization of GCPs into similar types and assess these individual categories in aggregate, as a similar degree of accuracy may be assumed to determine the coordinates of objects of similar categories while maintaining the same form of mapping throughout the province, which was generally met within the First Military Survey. In the experimentally tested area in northern Bohemia, mean errors achieved on individual types of GCPs were evaluated. It was categorized as follows: churches, farm-steads/courtyards/castles, mills, road crossings, other types of objects (bridging of water-courses, crossing of land cultures, etc.) Several foreign projects deal with the georeferencing of old topographic maps. The Mapire.eu website is a map portal showing available maps of selected European countries in a seamless view. In particular, detailed topographic maps made during the 18 th and 19 th centuries are included, while seamless georeferencing makes it possible to display an extensive part of Europe as a large summary map, which has no analogues between contemporary map projects. One of the layers available on the portal is the First Military Survey of the Habsburg monarchy. Georeferenced layers connected into a seamless mosaic are stored in the form of TLS map services and available within the Mapire.eu portal as separate map layers according to individual periods. Already on the basis of a visual comparison of the map layer published on Mapire.eu with the original sheets, it is evident that the territory was probably transformed in parts (triangular networks defined by GCPs or other per partes method), which is clearly visible in breakages of line objects, which appear abundantly within the maps (see Figure 3). Together with the knowledge of not as many GCPs used for the whole adjustment, this raises the question of whether georeferencing conceived in this way is sufficiently accurate and whether higher geometric accuracy could not be achieved by using global transformation with edge connection conditions and applying robust statistical methods to eliminate gross deviations, as outlined above. Thus, it is hypothesized that the adjustment of the IRLS method with the conditions of continuity of the edges of the map sheets leads to a lower total load of the resulting mosaic by geometric errors, which may stem mainly from a significantly higher number of identical points used. To verify this hypothesis, another group of control points (different from the original GCPs used for the initial adjustment) was collected, on which deviations of these points from the actual positions within both adjusted results were tested, i.e., both Mapire.eu maps and IRLS-adjusted mosaics.