 Geometry is the branch of mathematics dealing with spatial relationships,
measures, and properties of points, lines, and surfaces. In GIS applications,
vector geometry is used to represent the spatial component of geographic
features with discrete boundaries such as wells, rivers, states, streets, and
parcels.
The ArcSDE geometric model is centered around operations on various types of
geometric shapes, also called feature classes. Shapes represent geometric objects in two-dimensional planar
space that are useful for GIS applications. Shapes can be 0-dimensional points,
1-dimensional lines, and 2-dimensional areas. The available shape types in
ArcSDE are NIL,
Points, Lines, Simple Lines, and Areas. Each shape has a spatial reference
system which describes the coordinate space in which the shape is defined.
The spatial reference system for a shape describes the
coordinate system in
which it is defined. Spatial data often is defined with different coordinate
systems. To integrate spatial data from various sources, the data must be
transformed to a common coordinate system. The spatial reference system must be
clearly defined not only to verify the integrity of geometric calculations
between shapes, but also to allow transformations to take place between shapes
in different coordinate systems.
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