Model

{{Article
 * Author=Brian Bunker
 * Editor=Robert McCleary
 * BoK Topic=AM5, DA4
 * 311 Week=2
 * Tags=database design, ArcGIS, process automation
 * Content=A geographic model is a representation of some part of the physical world. Models are not perfect, in that they are not exact replications of reality.  A model is a "good enough" representation depending on it's application.  We create various layers of models in order to interpret and convey information.  We interpret the world with conceptual models.  Each person has a different conceptual model based on individual differences.  We create logical models to describe our conceptual models in preparation to implement another model: the physical model.  A physical model is the way that the logical model is coded and resides in a computer (for GIS data).

In GIS, a model could mean more than one thing. First, data models define the way that the data is treated by the GIS. There are two common data models in GIS; Raster and Vector. Data models tell the GIS how to interact with the data. Raster data are treated as rows and columns of cell values while vector data are points, lines and polygons.

http://gis.nic.in/gisprimer/images/vector.gif - Vector vs Raster Data Models - National Informatics Centre, India

In ArcGIS a model is a predefined series of tasks to be performed on given data. Models can be saved and reused to perform the same tasks and/or calculations repeated exactly any number of times. In ESRI's ArcGIS suite, models are created in ModelBuilder. Each task in model builder is given a specific tool. These tools are then "chain[ed} together..., using the output of one tool as the input [of] another tool". Models range in complexity from just a couple tasks to hundreds of tasks.

http://webhelp.esri.com/arcgisdesktop/9.2/published_images/Stage1d.gif - A Simple Model - ESRI, Inc.

http://webhelp.esri.com/arcgisdesktop/9.2/published_images/gory_model1.gif - A Complex Model - ESRI, Inc. }}