# Spatial Analysis for Landscape Changes: A Bibliometric Review
## 3 Results
### Co-Occurrence Map of Keywords of the Whole Period  
Concerning the co-occurrence map calculated in the period between 2016 and 2020, four main clusters were found. The prevailing keywords of these clusters are the following (the number of the cluster is just nominal, not ordinal):  
* Cluster 1 (Figure 5a, red cluster, a total of 40 items): the keyword with the most occurrences is climate change (1323). Here, secondary terms, besides the word climate (349), express the different aspects of landscape connected to climate change, from vegetation (573) to soil (146) and its erosion (97).
* Cluster 2 (Figure 5a, green cluster, a total of 69 items): the \"head\" or main terms are biodiversity (769 occurrences), pattern (896), and conservation (778), while minor terms are diversity (428), ecology (330), fragmentation (367), landscape ecology (152), habitat (231), connectivity (190), and landscape connectivity (86). It is interesting to note that the keyword \"spatial autocorrelation\" (94) was inserted in this cluster instead of the \"method\" cluster (the Cluster 3), even if, of course, the link with it remains through keywords GIS, land-use change, remote sensing, and, most of all,  
Figure 2: Tree map of the first twenty Web of Science categories where the works about spatial analysis for landscape archaeology are published.  
urbanization, which is strictly linked with topics such as the protection or conservation of biodiversity.
* Cluster 3 (Figure 5a, blue cluster, a total of 62 items): here it is possible to highlight two sub-clusters. The first one is prevalently a methodological one, with the main terms GIS (502) and remote sensing (427). The second one is more related to the urban and planning application fields, represented by the main words land-use change (666) and urbanization (431). Terms linked to both are representative of the types of analysis conducted and the instrument used, such as classification (359), the different names of remote sensors, change detection (104), spatial metrics (44), and simulation (165). Moreover, other secondary terms explain where these methods are applied: for urban growth studies (117) and urban expansion (79).
* Cluster 4 (Figure 5a, light green cluster, a total of 40 items): the main word is landscape (1172), while secondary terms are management (560), impact (629), ecosystem services (362), indicators (170), and vulnerability (112). As it is also possible to see from the other minor terms, it is a cluster more oriented to the evaluation of landscape resources, sustainability, and resilience.  
Figure 3: Spatial distribution of the countries of article authorship (**a**) in the World and (**b**) in Europe. World background taken from @ naturalearthdata.com. The graph was extracted using QGIS software.  
Figure 4: Co-authorship cluster map. Graph obtained by VOSviewer software.  
Figure 5: \(Cont\).  
By \"main word\", we meant words with the major frequencies clustered by the software.  
Together with the co-occurrence map, we extracted a map where the overlay between terms and the citation year is shown (Figure 5b): it shows the most cited keywords over the years. In the legend, in particular, the years between 2012 and 2016 are highlighted because this is the temporal range with the largest number of citations. In particular, the most recently cited keywords since 2016 are climate change and ecosystem service, while \"older\" ones (and actually, they are still consolidated in the literature) are GIS and remote sensing.