Degree of site suitability measurement in a GIS: The effect of various standardization methods

Suitability analysis is performed to identify sites (usually grid cells or pixels) suitable for a specific purpose so that management decisions can be made in a site-specific manner. However, sites identified as suitable are rarely equally suitable in the real world. Measurement of the degree of site suitability (DoSS) is therefore crucial to be able to manage sites in a truly site-specific manner. Conventionally, site suitability analysis is performed using weighted linear combination (WLC) of standardized input factors within Geographic Information Systems (GIS). Input factors used in such analysis can be standardized in a number of different ways. The method of standardization used in the analysis could have varying effects on the DoSS measurement. However, it is yet to be assessed and quantified. Therefore, the objective of this study was to quantify the effect of various standardization methods on the DoSS measurement. In this study, the DoSS of agricultural field was measured for site-specific application of animal waste as fertilizer. Seven input factors were used in the analysis. They were standardized using a) Boolean logic, b) discrete classification, and c) continuous rescaling methods. The Boolean logic method of standardization classified factor attributes as either ‘suitable (with class weight of 100)’ or ‘unsuitable (with a class weight of zero)’. The discrete classification method of standardization grouped attributes in up to five classes of approximately equal class size. These classes were weighted with equally-incremented class weights that added up to 100. The continuous rescaling method of standardization rescaled the range of attributes in a suitability value of 0 to 100. Standardized input factors were combined respectively using a WLC model to produce composite suitability maps. The DoSS of the composite maps were assessed using weighted average (WA), coefficient of variation (CV), and value range (VR) parameters. Standardization using Boolean logic method was of no consequence since it did not produce different degrees of site suitability. All suitable grid cells were equally suitable (i.e. WA= 700, CV=0 and VR=0). The discrete classification method of standardization produced diverse suitability values with weighted average ranging between 221.9 (CV=6.3 & VR=100) and 700 (CV=0 & VR=0) depending on the number of classes. This has highlighted the measurement inconsistencies of this method of standardization. Further investigation is therefore essential to quantify the effect of discrete classification method of standardization on the DoSS measurement. The continuous rescaling method produced a DoSS map with a WA of 419.05 (CV=8.04 & VR=332). This method of standardization is more consistent in the DoSS measurement and hence potentially useful for future DoSS assessment. However, there is a need to further assess the effect of rescaling using different attribute endpoint values on the DoSS measurement.