# The Impact of Spatial Resolutions on Nature-Based Solution Suitability Mapping for Europe
## 3 Materials and Methods
### Suitability Mapping Based on Multi-Criteria Analysis  
The method of multi-criteria analysis (MCA) offers the possibility to integrate a larger number of criteria that need to be considered for assessing the suitability of an area. As introduced above, NBS are selected based on different suitability criteria. MCA enables the integration of all criteria. Similar to the method used by other NBS decision tools [5; 7; 11; 12], for the MCA suitability mapping, the layers for each criterion are overlaid to identify areas where all criteria are met. GIS-based MCA methods offer three ways for overlaying layers [40], as follows: (1) Boolean; (2) weighted; or (3) fuzzy memberships. For this study, the Boolean method was chosen to be most suitable, and was used in this study. _Creation Boolean layers._ For the MCA, all input layers were transformed into Boolean layers. In particular, the CLC and LUISA land cover layers, as well as additional raster layers (soil depth, bulk density, soil texture, tree cover density, and buildings), were reclassified (according to the criteria outlined in Table 1) to a binary scale with values of 0 and 1, of which the value of 1 indicates suitable areas. For the OSM vector layer, suitable land covers were filtered and extracted. Intermediate results are presented as follows in Figure 3, which displays the suitable areas indicated by the three LULC layers: Figure 3a (LUISA), Figure 3b (OSM), and Figure 3c (CLC). _Boolean multi-criteria analysis._ The first part of the MCA was performed with the Boolean AND tool. This intermediate output layer (Figure 3d) shows all suitable areas where all criteria are met (except LULC layers). Following this step, the intermediate layer was overlayed with each of the three binary LULC layers. To include vector layers in the Boolean MCA, a different approach was adopted, since the Boolean AND is a raster tool. Hence, the filtered OSM layer was used to extract suitable areas. After this process, three output suitability maps were available, one for each of the three LULC layers. To further exclude transport lines, the OSM line vector layers of roads, railways, and transport were merged and buffered with 3 m. With this resulting layer, suitable areas located on these transportation lines could be removed with the erase tool. Similarly, the EU-Hydro layers \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Layer** & **Suitable Criteria** & **Spatial Resolution** & **Temporal Range** & **Source** \\ \hline LULC: Corine Land Cover (CLC) & Agriculture, pastures, natural grassland, & 100 m & 2017–2018 & [41] \\ \hline LULC: LUISA Base Map (2018) & sparsely vegetated areas, burnt areas, and & 50 m & 2017–2018 & [42] \\ \hline LULC: OpenStreetMap (OSM) & (broad-leaved) forests & n/a & 2022 & [43] \\ \hline Tree Cover Density 2018 & 0–20\% forest density retention threshold & 10 m & 2018 & [44] \\ \hline Buildings (European Settlement Map (ESM)) & Areas without buildings & 10 m & 2015 & [45] \\ \hline Roads, Railways, Transport & With a 3 m buffer & n/a & 2022 & [43] \\ \hline Soil Depth & \textgreater{}60 cm & 250 m & 1950–2015 & [46] \\ \hline Bulk Density & \textless{}1.6 g/cm & 500 m & 2009 & [47] \\ \hline Soil Texture (USDA) & soils with efficient water intake: sandy loam, loamy sand, sandy clay loam, loam, silty loam silt loam, and clay loam & 500 m & 2009 & [47] \\ \hline EU-Hydro & Buffers around water areas: & & & \\  & Canals/Ditches = 5 m & 1 ha & 2006–2012 & [30] \\  & Rivers (line) = 15 m & & & \\  & River (polygon) = 30 m & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Input layers for the suitability mapping of riparian forest buffers. were merged and buffered with different buffer widths depending on the type of waterway (see Table 1). Finally, suitable areas within the water buffer could be extracted. Exclusion of fragmented areasThe three resulting output layers show suitable areas along rivers, streams, ditches, and canals.