# Separating Built-Up Areas from Bare Land in Mediterranean Cities Using Sentinel-2A Imagery
## 5 Results and Discussion
### Results for the Main Study Region
These problems were also observed in other built-up, index-based combinations (Figure 9c). The NDTI, in combination with the NDVI and the MNDWI determined the industrial regions more precisely. In such a heterogeneous region, a multi-index image of NDTI, NDVIre, and MNDWI provided superior information about all land cover classes, compared to the other classification results (Figure 9d). Figure 8: (**a**) RGB image of the Sentinel-2A; (**b**) the classified Sentinel-2A; (**c**) the classified multi-index (NDBI, NDVIre, and MNDWI); and (**d**) classified multi-index (NDTI, NDVIre and MNDWI) images. Figure 9: (**a**) RGB image of the Sentinel-2A; (**b**) the classified Sentinel-2A; (**c**) the classified multi-index (NDBI, NDVIre, and MNDWI), and (**d**) the classified multi-index (NDTI, NDVIre, and MNDWI) images. Generally, the multi-index image of the NDTI, NDVIire, and the MNDWI successfully separated bare land from the built-up areas, while categorizing other land cover classes, such as vegetation cover and water body precisely (Figure 10d). Classification of the NDTI-based multi-index set provided a superior understanding of the built-up area patterns and building footprints, especially for the organized types of residential construction (Figure 10(II,IV,IX)) and avoided an overestimation of the built-up areas in the classified Sentinel-2A image (10 bands) (Figure 10b). The other multi-index  
Figure 10: (**a**) RGB image of the Sentinel-2A; (**b**) classified Sentinel-2A; (**c**) classified multi-index (NDBI, NDVIre, MNDWI); and (**d**) classified multi-index (NDTI, NDVIre, MNDWI) images. Regions illustrated: (**I**) Eyup-Gokturk; (**II**) Avicular; (**III**) Gumusdere; (**IV**) Beykoz; (**V**) Bahcelieyler; (**VI**) Eyup-Akpinar, (**VII**) Beyoglu; (**VIII**) Esenyurt; (**IX**) Sariyer-Uskumrukoy; and (**X**) Umraniye districts. image generated using the NDBI, the NDVIIre, and the MNDWI, using the NDBI as the nominee of the existing built-up indices had an excessive misclassification issue. It classified bare land cover as the built-up class and vice versa (Figure 10c). Farmlands with no vegetation cover and low water content and especially those that were compacted because of the field operations, heavy equipment, and tillage implements were mostly misclassified as built-up regions with the NDBI-based set. This misclassification problem was mostly overcome using the proposed NDTI-based multi-index image (Figure 10 (VIII)). Bare land cover near asphalt roads, which also contained a lower water content, were among the land cover classes that were highly misclassified as built-up areas, and this problem was significantly improved by using the NDTI-based multi-index image (Figure 10(III,VI,X,IX)). Although, the classification results of the NDTI-based multi-index image underestimated the density of the built-up area in some dense built-up regions, the proposed multi-index image classification method provided reliable information about both bare land and built-up classes, while accurately categorizing water and vegetation land cover classes.