**3. Results**

#### *3.1. Overview of the Planning Articles Reviewed*

Among the 67 planning articles reviewed, the number of articles that contained objective formulation, type/scenario evaluation, quantity/scale determination, and site selection is 60, 58, 14, and 20. It is known that objective formulation and type/scenario evaluation are the hotspots of GSI planning at present, while the planning approaches that considered quantity/scale determination or site selection are less than one-third of the articles. In addition, there were only 3 articles that contain all planning steps, and 16 articles with consideration of 3 steps, while most (43) articles included 2 steps, 33 of which dealt with the objective formulation and the type/scenario evaluation. The remaining five articles only carried out a single step. Therefore, the current GSI planning is fragmented and the planning steps considered are not consistent and comprehensive in articles, which may limit the development of GSI planning and construction. It is therefore insightful to identify the research gaps of the planning steps from the facility perspective. A detailed description of the distribution of planning steps considered in these articles, and a detailed discussion of each planning step, are carried out in Sections 3.2–3.5.
