Suitability analysis, or site selection, is a GIS-based process used to determine the appropriateness of a given area for a particular use. The basic premise of suitability analysis is that each aspect of the landscape has intrinsic characteristics that are in some degree either suitable or unsuitable for the activities being planned. Suitability is determined through systematic, multi-factor analysis of the different aspect of the terrain. Suitability analysis can be performed using either vector or raster data, but is often performed using the latter. Different data layers are created which correlate to various physical, cultural, or economic factors that would be important for site selection analysis. The results are often displayed on a map that is used to highlight areas from high to low suitability.
A suitability model typically answers the question, "Where is the best location?" — whether it involves finding the best location for a new road or pipeline, a new housing development, or a retail store. Often, a Multi Criteria Evaluation approach is required in order to answer this question. Multi-criteria evaluation is the the process by which a set of known project criteria are explored, ranked and/or weighted, in order to find the best outcome. For instance, a commercial developer building a new retail store may take into consideration distance to major highways and any competitors' stores, then combine the results with land use, population density, and consumer spending data. This information would be ranked based on its importance to the store's success. Some of the criteria might be absolutely essential, while others may not be so vital, though certainly of benefit. This data could then be weighted based on these rankings, allowing for the vital criteria to be met first. The developer would then come up with a group of locations that meet all, most, some, or none of the criteria, allowing them to choose the best location for the store.
Decision making using suitability analysis can be discrete, when it is analyzed with a finite set of alternatives or continuous when it is analyzed with an infinite number of alternatives. In general terms, discrete suitability analysis is based on the construction of a matrix that reflects the characteristics of a set of election alternatives which are derived from a set of specific criteria. Such matrix can be called effectivity matrix, evaluation matrix or simply decision matrix. This decision matrix expresses the qualities (in numeric or symbolic terms) of the alternatives with respect of the attributes considered in the analysis. If the criteria used in this process are numeric, then they are called quantitative, and when they do not represent a numeric measure they are considered qualitative. Once the matrix has been built, it is possible to apply some evaluation procedure which will allow assigning a value to each alternative, reflecting the way in which they answer the original geographic question of the analysis.
- Land Use Analysis: Most jurisdictions use land suitability analysis for site selection, impact studies, and land use planning.  Generally the output of the analysis can be used to determine policy in regards to specific city ordinances and regulations. The goal with most suitability analysis done with land use is to find under-utilized and vacant land to further develop. The analysis provides information on the current land use of such sites as well as local utilities access and development patterns. Land use analysis helps cities learn where about areas they can afford to grow and areas that need redevelopment.
- Retail Site Selection: Suitability analysis is critical for both marketing and merchandising purposes, as well as for choosing new retail locations.
- Agriculture: Used extensively to find and maintain good cropland as well as ensure proper crop rotation. It is also used to determine areas of open range cattle areas and where areas need vegetation recovery. Suitability analysis of croplands helps to ensure that land resources are used in the most productive and sustainable ways. Different crops require different land types and growing conditions; for example, land that is suitable for growing corn may not be appropriate for growing rice or other crops. A suitability analysis of agricultural land using GIS is useful because it provides a way to look at many different layers of data for a given area. A GIS user can look at layers such as soil type, average rainfall, topography, and many others, and use this information to determine whether or not a given piece of land is well-suited for different agricultural practices.
- Defense: Suitability analysis is used in defense in many different ways. It is essential in construction of bases and military outposts to find the most strategic location. It is used to find the safest route for convoys and transport ships. It can also find the most suitable areas of enemy strongholds and encampments. These analyses of military and defense applications rely heavily on Remote sensing.
- Crime Analysis: Determines areas of crime rate based on spatial data. Can be used by law enforcement and city officials to locate areas of high crime and other problem areas. With this information city officials can focus on helping specific parts of their city and locate general targets for criminals. Additionally, it can be used by law enforcement to search for patterns in both type and quantity of crimes by utilizing the tools and methodology of Spatial Analysis.
- Spatial Analyst is an optional extension to ArcGIS Desktop that provides users the ability to build complex site location analysis models.
- Signature Analyst is a geospatial predictive modeling tool used to conduct suitability analysis.
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- Spatial Analyst
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