Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Vector-Based Geographic5 Datasets—Logical Construction

Geodatabases and coverages are the two most sophisticated data structures used by Esri software. They are sophisticated in different ways, as you will see later. The coverage concept dates back many years and was the foundation of ArcInfo–lines that represented linear features and that separated polygons were call “arcs.” The geodatabase is a more recent development. You will spend a fair amount of time and effort understanding and working with geodatabases. The coverage data structure is, frankly, rapidly becoming obsolete. My recommendation is that GIS professionals of today convert their coverages (and, admittedly, there are a lot of them around) to the File Geodatabase structure. Another data structure, the middle-aged shapefile, is relatively simple, but because multitudinous data sets exist in this form, nationally and internationally, it is also important. Understanding geographic data structure is vital to being able to do some forms of analysis with GIS. Please note that you can convert any of the three of these dataset forms into any of the others.

The primary elements of vector-based datasets are points (zero-dimensional entities), lines (one-dimensional entities), and polygons (two-dimensional entities). Terms used with all Esri data models are described in the sections that follow, and then when we look at particular data models. Figures that graphically show the entities follow in the detailed discussions of geodatabases ...