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A gravity hill is defined as such a location where the layout of surroundings produces an optical illusion which makes a downhill road appear uphill. The major factor which contributes to this illusion is the obstructed horizon. Without a horizon, which is a reliable reference, it becomes difficult to judge the slope of a surface as it is not visible. There are many such places existing on Earth which have already been discovered. Bressan et al. (2003) has listed various locations of such spots which are famous and exist around the world with around 15 of them only in United States and Canada. All such places are famous either for supernatural activities, magnetic powers or even secret military projects (Benecke, 2002; Polidoro, 2007).
Very less literature has been found on the topic of gravity hills. Most of the literature which is available discuss about the illusions and out of those, very few have discussed illusion due to slopes. Proffitt et al. (2001) did a lot of experiments on the perception of slants of hills. Their experiments concluded that the slant perceptions are always grossly overestimated. Bressan et al. (2003) have directly worked on the gravity hill phenomena by recreating the models of various gravity hill spots. They concluded that the gradient of the roads is misperceived due to the absence of a reference line or horizon and also that this phenomenon is easy to be recreated artificially without putting any external force of magnetism or antigravity. Stefanucci et al. (2005) has discussed about the appearance of distance on sloping areas and more precisely on the hills. He concluded that the distances appear more on hills, but his research is based on pedestrians walking uphill or downhill. Tsuinashi (2008) did an experimental work related with optical illusions by using pitched rooms and pitched floors. His experiments concluded that the vertical gradient of the roads or any surface in view could be misperceived and can work as an illusion. Kitaoka (2015) has discussed illusion on a gravity hill by using diagrams and included a case study of such spot in Radan, Serbia. Jaf (2009) has studied one such spot in Koya region, Kurdistan-Iraq. He performed visual inspections and took photographs to prove the phenomena of gravity hill existing within a small 200m section of road. Hengl et al. (2008) used around 2,000 data points to create the DEM of an area to study its hydrological and land cover properties by using maps.
Regarding the reliability of geospatial data obtained from Google Earth (GE) Pro 2018 for the study in this research, Mohammed et al. (2013) performed a comparison of the data obtained from GE with the data obtained by using a Global Positioning System (GPS) device. After performing statistical analysis testing they concluded that the data obtained from GE can be used for investigation and preliminary studies with suitable accuracy. In a similar kind of a study, Rusli et al. (2014) compared the DEM generated by using three different geospatial data sources including GE, Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topography Mission (SRTM). They created separate DEMs for flat, hilly and mountainous regions and for each section they took around 5,000 data points. After performing the correlation analysis, they concluded that the DEMs formed by using the data of GE were closely related to the DEMs generated by the other two sources and the data of GE is completely reliable to be used for any geospatial or geomorphological studies.
To the best of the author’s knowledge, no scientific study involving geospatial data by using Digital Elevation Modelling was found for any of the gravity hills in the world. The existing studies consists of visual analysis through photography, existing maps and preparation of physical models, as cited earlier. Many news articles were studied on various websites where people have been discussing gravity hills, but the information provided there is neither authentic nor supported by any evidences. Hence after studying all of the available data it was found necessary and need of the time to have an investigation of a gravity hill based on geospatial data in order to get scientific evidences for people to understand the phenomena and the reason of movement of rolling objects uphill or on flat surfaces on their own.