We usually think of a ‘model’ as a way of representing the world. But the term model can be a bit confusing in the GIS world. There are data models – a way of representing the world in a database. We have many ways of representing the world in a GIS database – points, lines, polygons, images, surfaces and 3D volumes are the most common but there are many variations on these basic building blocks. In recent years standard data models have been developed to encompass common concerns in particular domains. ESRI and other organizations have published data models for transportation, land records, hydrology, telecom, water/wastewater, to name just a few. Contemporary software is usually structured in terms of objects. Object models help us to represent the world in a software program.

A third type of model represents our world in terms of processes. In this sense, a GIS model is a sequence of processes that generate a measurement, create a map, transform existing data sets into new ones or run repeatedly to create a simulation. The objectives of a process model can vary broadly. Very commonly, a model is simply a way to automate a sequence of actions that we would otherwise have to perform manually. In other cases, the model may be generating a measurement or other output for a particular set of inputs.

Azavea has worked on a few projects that were composed almost entirely of this type of model. The Natural Lands Trust developed the SmartConservation model, a methodology for scoring any location in SE Pennsylvania by calculating more than 40 different conservation and landscape ecology metrics. These scores were combined into a single SmartConservation score for a property that indicated its conservation value. Azavea wrote software using ArcIMS and ArcObjects to automatically calculate these metrics with only a web browser.

These types of models have existed on paper for as long as people have been using GIS software, but it become much easier to chain together a series of operations with the advent of flowchart-style tools now present in several GIS software packages. In the ArcGIS environment, models are created by either writing a script or using ModelBuilder. ModelBuilder is a visual programming language that enables an ArcGIS user to drag data sets and GIS processes onto a drawing surface where they can be connected together and turned into sequences of operations. The models (which are also known as ‘tools’) can be strung together into larger models, can be shared amongst users with common data sets and can even be published on the web using ArcGIS Server.

When I founded Azavea seven years ago, one of my dreams was to make the process of building and executing GIS models easier. Are there processes you would like to automate or geographic models you would like to build? Give us a call.