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For this initial run, the criteria addressing peat slope angle > 15º was modelled. All peat mapped in the subsoilsmap was used in the classification process as shown in Fig. 5.3. The input maps to the classification processare shown in Fig. 5.4. The data was combined in the GIS using established map algebra techniques.Fig 5.3 Model schematic for first susceptibility mapThe output of this first run susceptibility map production is shown in Fig. 5.6. The susceptible areas in this firstrun have been enlarged by a factor of 5 for display purposes. With this exaggeration factor taken into account,examination of the output shows that there is a relatively low percentage occurrence of susceptible areas asdefined by the modelling process.Further examination of the inputs shows a low occurrence of peat areas in the subsoils map on slopes > 15º.This situation results directly from the nature of the classification scheme employed in the production of thesubsoil maps. The category referring to rock was mapped based on the general classification criteria of rockbeing at or close (within 1 metre) to the surface. For soil classification purposes in traditional soil survey, peatsoils are characterised by being at least 30cm in depth in a drained state, and 40cms in depth in an undrainedstate. The situation therefore arises where areas mapped correctly as rock in the subsoils map of Mayo wouldappear equally correctly as peat on the published NSS soil map. Both maps are essentially correct in theseareas in terms of the classification schemes employed in the mapping efforts.While initially appearing problematic, this situation can be used to improve the use of the data available for thiscase study. This results from the fact that the published soil survey map, if considered to be more resolved inthe sense that survey was primarily field based, can be used to assess the other data inputs. A revisedcombination of data can then be employed in the production of a landslide susceptibility map. Fig. 5.5 showsthe NSS soil map of West Mayo and peat landcover classes from the EPA Soil and Subsoil landcover map.Each of the subsoil classes was examined in relation to the landcover map and the published NSS soil map ofWest Mayo. Subsoil classes were reselected on the basis of their spatial co-occurrence with peat landcovertypes. This subset of subsoil types was tabulated according to the spatial overlap on mapped soil types fromthe NSS soil map.NSS Soil MapSubsoil class co-occurring with peat type landcoverRck TQz TGr TMpPeat 56 77 58 64Peaty Podzol 37 17 23 30Total 93% 94% 81% 94%Table 5.4 Relative percentages of particular subsoil categories and their associated mapped NSS soil classes.The subsoil classes are:Rck = rock at or near the surfaceTQz, TGr, TMp = Tills predominantly composed of Quartzitic, Granitic and Metamorphic materials respectivelyFrom this analysis it is clear that the use of the peat category from the landcover map in conjunction with theadditional classes from the subsoils map as detailed above could provide an enhanced predictive map of peat40