Geocomputation is a cutting edge research area within the field of GIS and geospatial analysis. For this reason it is strongly influenced by recent developments in programming, data processing and interface design. Nowhere is this more apparent than in the concern for modelling of dynamic process.

Current commercial and public domain GIS software systems all contain numerous tools for acquiring, pre-processing, and transforming data. Their use in modelling includes data management, format conversion, projection change, re-sampling, and raster-vector conversion. GIS also include excellent tools for visualisation/mapping, rendering, querying, and analysing model results, as well as assessing the accuracies and uncertainties associated with inputs and outputs.

Typically, all of the capabilities described above are accessible via end-user graphical and command line interfaces. However, these capabilities have recently become accessible through Application Programming Interfaces (APIs), via software libraries. The exposure of GIS APIs is a significant recent improvement, as external programmers now have access to the underlying software components upon which GIS software vendors base their systems. This is perhaps the most pertinent enhancement, as many of the techniques used in GIS analysis are more robust if they can be linked with an extensive toolkit of methods for simulation (see further, Section 8.1.2.2).

Recently in GIS there has also been a move to use industry-standard programming languages (e.g. Java, C++, and Visual Basic), and scripting languages (e.g. Python, VBScript, and Jscript) rather than proprietary, home grown scripting languages (e.g. ESRI’s Arc Macro Language, AML, or Avenue). Interoperability standards such as the Microsoft .NET framework facilitate this process by allowing compliant packages to be called from the same script. In addition to scripts, graphical flowcharts can be used to express sequences of operations that define a model. One of the first graphic platforms for conceptualising and implementing spatial models was the ERDAS IMAGINE software, which allows the user to build complex modelling sequences from primitive operations. ESRI’s ArcGIS and Idrisi Andes are other examples of GIS products that allow models to be authored and executed in a graphical environment.

In principle, graphic-model building can be used for dynamic modelling via an iterative process, where the output of one time-step becomes the input for the next. However, this method poses two problems:

1) the GIS will not have been designed for an iterative process, requiring the user to re-enter the data at the beginning of each time step, and

2) the time required to run a model can be considerable

The former of these problems can be overcome with scripting languages; both can potentially be overcome by integrating the GIS with a simulation/modelling (s/m) system better equipped for the task at hand. Before exploring the possibilities of linking GIS and s/m systems, the following subsection 8.1.2.1 evaluates the capability of GIS to handle space-time information, which computer simulations generate in volume.