Data models and structures

Descriptive attributes can be described as being spatial or non-spatial, though the difference between them may be subtle and ambiguous. There are two basic types of structure used to represent the features or objects. These are raster and vector data, and as a consequence, there are different types of GIS software architecture, and different types of analysis, that have been designed in such a way as to be most effective with one or other type, such as Idrisi or ERDAS Imagine (raster) and MapInfo or ArcGIS (vector). Raster data represents a regular grid or array of digital numbers, or pixels, where each has a value depending on how the image was captured and what it represents. Data may have been digitised in vector form but subsequently needed in raster form for input to some multi-criteria analysis.