May 2002
Beginner to intermediate
448 pages
13h 18m
English
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19.4 Special Standardization Elements
Spatial representation
Geographical objects are represented spatially as either vector or raster data. Vector data consists of the geometric primitives points, lines, and areas, and the topological primitives links, nodes, and faces. Raster data is based on the division of the real world into small, uniform units (cells). At the superior level, standard schemas should be developed to describe the geometric and topologic primitives. This will increase the ability to share geographic information among applications. These schemas will be useful for geographic information system and software developers and users of geographic information in providing consistently understandable spatial data structures. Today ISO and other organizations are working on the description of conceptual schemas for the spatial characteristics.
At the application level a geometric primitive—point, line, area or raster cell—has to be specified to represent each object type. The cell size must be specified for raster data, and rules must be established for the creation of nodes and links for vector data.
Spatial referencing
Spatial referencing can be based on referencing by coordiantes or referencing by geographical identifiers. An object is not clearly georeferenced without being linked to a coordinate reference system. The most important elements in a coordinate referencing system are a datum—specified with ellipsoid, anchor point, and prime meridian—and the coordinate ...
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