## 3 Study Area, Database, and Previous Research  
The Tirano South study area, whose location is shown in Figure 1, occupies the southern half of a community area termed \"Comunita Montana Valtellina di Tirano\" in the Province of Sondrio, Lombardy Region, in northern Italy. It was established in 1971 for socioeconomic and environmental protection (www.cmtirano.so.it; accessed on 7 April 2021). The geomorphology and landslide processes in the area were described by [PERSON] (2008) [16], who compiled the available information and constructed a database for an initial landslide susceptibility analysis. Part of the data is being used in this contribution that also covers the same study area. Elevations in this young Alpine geology area range between 300 and 3000 m a.s.l. and rainfall from 700 to 1900 mm, thus providing different climatic conditions. Vegetation consists of broad-leaved forests at lower elevations andiferous forests at higher elevations. The geomorphology is controlled mostly by glacier activity, but anthropic activity significantly affects land use at valley bottoms with tourism, agriculture, and industries. Glacial and torrent erosion, together with intense rainfalls, are the triggers of slope instabilities. Out of a variety of landslide phenomena in the area, 70 active landslides were identified from published inventories. However, they did not contain sufficient information for separating rotational from translational dynamic types. In addition to the inventories used to generate digital images of landslide trigger area locations, various cartographies related to slope instability were available for compilation and digitization into the database, as shown in Figure 2. The database offers opportunities for experimenting on spatial prediction modeling of landslide susceptibilities, hazards, and risks. Figure 1: Locations of the Tirano South study area, in the Lombardy Region, northern Italy. The Tirano South database consists of digital images within a raster of 1090 pixels by 1194 lines with 20 m resolution. The study area proper within the raster covers 646,091 pixels corresponding approximately to 258 km\({}^{2}\). The trigger zones of the 70 active landslides, converted into DSP and abbreviated as **70 at**, cover 697 pixels, i.e., as a training area (TA) a little less than 0.11% of the study area (SA). Eight cartographies are used to generate, at the same 20 m resolution, the ISPs consisting of maps with 23 land use classes, **u**1-23, with 51 geologic (lithologic) units, **I**1-51, and with eight permeability classes, **p**1-8 (three categorical maps), in addition to aspect (0\({}^{\circ}\) to 359\({}^{\circ}\)), **A**, topographic curvature (\(-\)32 to +29), **C**, topographic digital elevation (350-2906 m), **D**, internal relief (0-111 m for 3 \(\times\) 3 pixels), **I**, and slope (0\({}^{\circ}\) to 61\({}^{\circ}\)), **S**, all derived from a 5 \(\times\) 5 m resolution digital elevation model, DTM, resampled to 20 \(\times\) 20 m (5 continuous field maps). Previous research by [PERSON] and [PERSON] (2007) [17] on landslide susceptibility in the Tirano area used an earlier and simplified database with 28 active complex landslides and five binary and binarized factor maps applying the weights-of-evidence mathematical model and generating arbitrary thresholds of prediction ranks. That and similar applications of spatial prediction modeling were criticized [18] so that in joint contributions that used the same database, kindly shared by those authors, cross-validation procedures were preferred. The purpose was to assess the relative quality of the modeling results with an alternative model and different analytical processes that exposed the uncertainties associated with the prediction patterns [19; 20]. A further study with a wealth of controlled information on Alpine landslides and three national-regional mapping initiatives provided new data for the construction of a high-quality database for the Tirano study area.