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Similarity Analysis


Similarity Analysis assesses the degree to which a given case study site is similar to other areas of Earth’s land in terms of a set of global variables selected by the user.

Purpose: To determine which areas of the world have similar conditions to a given case study.  Similarity analysis is designed to help case study researchers make stronger regional and global inferences from their work and to facilitate collaborations with colleagues across similar conditions around the world.

Why use it:  To make case studies more globally relevant and to find and share knowledge with colleagues working under similar conditions around the world.  The results of local case studies can be relevant across larger areas, and case study researchers can learn from results and expertise at other sites, especially when their conditions are similar (e.g. similar population densities, land use, soils, climate).  Similarity assessment quantifies how similar a given study site is to other areas of the world in terms of a global variable or variables, highlighting the potential global relevance of a case study in terms of a mapped and measured global extent, thereby helping to support inferences at regional and global scales, while identifying additional case studies and colleagues working under similar conditions around the world.

How it works:  Similarity analysis is based on the principle of statistical distance measurement (normalized Euclidean distance).  For a given case study site, the similarity of other areas of the world to the site is computed and mapped based on their statistical distance, in terms of user-selected global variable(s), from the value(s) at the site.  Similarity varies from 0 to 1, with 1 being most similar, and global areas with different levels of similarity to the site are calculated in km2.  The similarity of all case studies in GLOBE to the selected site is then calculated and presented as a ranked list, with the most similar case studies at the top.

How to use it:

  1. Select/View a case study and click on the Similarity Analysis icon.
  2. Specify the global extent (filter/delimit) that the case study should represent (e.g. tropical forests, population density < 10 persons km-2).
  3. Select global variables needed to characterize conditions at the case study site relative to other areas of the world.  For a case study of a densely populated remote agricultural landscape in the humid tropics, one might select population density, market access, cropland percent, and tropical forest potential vegetation.
  4. Run the Similarity Analysis.  Results are presented as statistics, histograms, and a map.
  5. Interpret the map. Areas most similar to the site are highlighted in green and areas least similar in red.  If areas that you know are different from the site are green (or similar in red), variables can be changed and the analysis rerun. The statistics window can be hidden by clicking the statistics icon.
  6. Interpret the histogram. The similarity histogram illustrates the distribution of areas within the specified global extent in terms of their similarity to the selected site (same colors as map).  A big green bar at the far right means there is a large similar area.  
  7. Interpret the statistics.  The global areas with different levels of similarity to the case study site are computed in km2 and % area.  At top is the entire delimited (filtered) extent (as % of global land area), followed by areas with increasing global similarity (as % of delimited area).
  8. Collect similar cases. Case studies in the GLOBE database are listed in order of their similarity to the selected case, with the most similar at the top.  Cases can be selected and added to a new or existing collection for later use or analysis.
  9. [Optional] If unsatisfied, rerun the analysis, changing the specified extent and/or variables.
  10. [Optional] Save the similarity analysis.  The analysis is must then be named and can be shared (web link) and/or resumed.
  11. [Optional] Publish the similarity analysis.  The analysis is saved in a permanent (unalterable) format serving as the document of record that can be shared in a citable format (permalink) or printed as a .pdf for inclusion as a supplement in published work.


References Cited

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