Store all related coverages in one common coordinate system. Spatially reference the features of each coverage against features in associated coverages. Ideally, each layer in a GIS represents one theme. Examples of themes are roads, rivers, soil type, temperature. Each of these are individual themes.
Themes help organize related features and maintains the database in a simple and manageable form.
Separating features into themes facilitates data update and facilitates analysis and display of information. Tiles also simplify databases by segmenting the study area into manageable units. These individual units allow ease of use, and increase in processing speed. Tiling systems must also allow for quick and simple joining of adjacent tiles. At the heart of any GIS is the coordinate system that ties graphical features to a position on the surface of the earth.