GIS专业英语lesson(DataAnalysis.docVIP

Lesson 22 data analysis  = 2 \* ROMAN \* MERGEFORMAT II Integrated Analytical Functions in a GIS Most GISs provide the capability to build complex models by combining primitive analytical functions. Systems vary as to the complexity provided for spatial modelling, and the specific functions that are available. However, most systems provide a standard set of primitive analytical functions that are accessible to the user in some logical manner. Aronoff identifies four categories of GIS analysis functions. These are : ? Retrieval, Reclassification, and Generalization; ? Overlay Techniques; ? Neighbourhood Operations; and ? Connectivity Functions. The range of analysis techniques in these categories is very large. Accordingly, this section of the book focuses on providing an overview of the fundamental primitive functions that are most often utilized in spatial analyses. Retrieval, Reclassification and Generalization Perhaps the initial GIS analysis that any user undertakes is the retrieval and/or reclassification of data. Retrieval operations occur on both spatial and attribute data. Often data is selected by an attribute subset and viewed graphically. Retrieval involves the selective search, manipulation, and output of data without the requirement to modify the geographic location of the features involved. Reclassification involves the selection and presentation of a selected layer of data based on the classes or values of a specific attribute, e.g. cover group. It involves looking at an attribute, or a series of attributes, for a single data layer and classifying the data layer based on the range of values of the attribute. Accordingly, features adjacent to one another that have a common value, e.g. cover group, but differ in other characteristics, e.g. tree height, species, will be treated and appear as one class. In raster based GIS software, numerical values are often used to indicate classes. Reclassifi