**5. GIS application in environmental study**

 Nowadays, the rapid developments of computer technology and geographical information system (GIS) are receiving increasing interest in environmental geochemistry study [81]. This method is becoming popular nowadays in marine environmental pollution studies to graphically and digitally present the distribution of metals in marine environments by using GIS technique [82, 83]. The spatial interpolation methods of geometrical interpolation, trend surface analysis, and kriging method are commonly used [84]. This base chemometric approach was applied to investigate the spatial distribution patterns of metals in marine sediment and to identify spatial human impacts on global and local scales [85, 86].

 GIS is a tool for decision-making, using information stored in a geographical form, in this case, in isopleth map form. Some researchers defined major requirements and function of GIS and mentioned spatial data handling tool for solving complex geographical problems [87, 88]. This GIS approach is increasingly used in environmental pollution studies because of its ability in spatial analysis and interpolation, and spatial interpolation utilizes measured points with known values to estimate an unknown value and to visualize the spatial patterns [89]. On the regional and national scales, the geochemical mapping of metals can be used as a tool for visualization which is enhanced by computer-aided modeling using GIS to make it easier to identify the possible locations of contaminated area. At present, joint using of GIS and chemometric approach mainly focuses on river estuary [90], soil [91], and nonpoint source identification [92].
