System of the 1:28 800 scale sheets of the Second Military Survey in Tyrol and Salzburg

Abstract

The Second Military Survey of the Habsburg Empire (Franziszeische Landesaufnahme) was based on the first triangulation net of the Empire, ordered by Emperor Francis I in 1806. Eight horizontal control points were later used as projection centers for the different parts of the Empire. However, two provinces, mapped in the very early phase of the survey, have no real terrain objects as projection centers. In spite of the earlier literature items, mainly concerning the cadastral systems, the map sheet systems of the Second Military Survey of Tyrol and Salzburg do not follow the Soldner-Cassini projections centered at Innsbruck and Gusterberg, respectively. Indeed, the design of these sheets is similar to the one of the First Military Survey in cartographic point of view also with respect to their projection. The systems of the 1:28 800 sheets in these provinces are not centered at Vienna (St. Stephen) or Gusterberg as it was indicated in the literature. Projection analysis shows that for these provinces a unified sheet system was introduced. It can be connected to an Innsbruck-Pfarrturm-centered Cassini projection but the projection center is not at any distinct point (sheet center, corner or boundary halving point) of the sheet system. This Cassini projection, however, is not suitable for precise georeferencing of the sheets of Tyrol and Salzburg as it results errors up to one kilometer. The map sheets of these provinces can be rectified using quadratic formulae with remnant errors of maximum 220 meters (Tyrol) and 500 meters (Salzburg), which are much higher values than the fitting accuracy of the sheets in other parts of the Empire. According to the analysis, Liechtenstein is also without definite projection center but it is covered by only one extended sheet and its rectification can be done with an accuracy of 30 meters.