De Smith and Goodchild [2] examined geospatial analysis process in the broader context of analytical methodologies. The typical process of geospatial analysis typically follows a number of well-defined and iterative stages:
In the whole, geospatial analysis can be seen as part of a decision process and support infrastructure. The process from problem specification to outcome is, in reality, an over-simplification, and the analytical process is more complex and iterative than the steps suggest. GIS and related software tools that perform analytical functions only address data gathering, analysis, and modeling. As de Smith and Goodchild point out, the flow from start to finish is rarely the case. Not only is the process iterative, but at each stage one often looks back to the previous step and re-evaluates the validity of the decisions made. Mackay and Oldford in de Smith and Goodchild [3]described a spatial analysis method in terms of a sequence of steps labeled PPDAC: Problem; Plan; Data; Analysis; and Conclusions. The PPDAC approach is shown in the below figure.
As can be seen from the diagram, although the clockwise sequence (1→5) applies as the principal flow, each stage may, and often will, feed back to the previous stage. In addition, it may well be beneficial to examine the process in the reverse direction, starting with Problem definition and then examining expectations as to the format and structure of the Conclusions. This procedure then continues, step-by-step, in an anti-clockwise manner (e→a) determining the implications of these expectations for each stage of the process.
PPDAC develops evidence. Evidence, in the context of this discussion, refers to the information that is gathered by exploratory analysis of spatial and temporal data. These methods include remote sensing and GIS to develop intermediate products. "Exploratory data analysis (EDA) is about detecting and describing patterns, trends, and relations in data, motivated by certain purposes of investigation. As something relevant is detected in data, new questions arise, causing specific parts to be viewed in more detail. So EDA has a significant appeal: it involves hypothesis generation rather than mere hypothesis testing" (Exploratory Analysis of Spatial and Temporal Data, Springer, 2006). Ultimately, what is evidence is defined by the intelligence producer. Ideally, "evidence" in the context of the framework of the problem should include: the context and the scientific and intuitive evidence.