Geography Reference
In-Depth Information
Polygon defined by
a single ring
Polygon defined by
multiple disjoint rings
Polygon defined by
multiple nested rings
FIGURE 4-12 Different configurations of a “polygon” composed of multiple enclosed areas
(500,708)
Polygon A
Area
Polygon D
Area
5
10
Perimeter
5
14
38
Perimeter
5
5
46
(500,704)
(512,704)
Polygon B
Area
Polygon C
Area
20
Perimeter
5
28
Perimeter
5
5
18
5
22
(500,700)
(505,700)
FIGURE 4-13 A simple topological diagram in geodatabase form
of built-in capabilities promote data quality. For example, suppose that you are building a database of
the roads in your county. One attribute in the database is the material the road is made of. Perhaps you
know that the only allowed materials are concrete, asphalt, macadam, and gravel. With geodatabases
you could allow a data entry person to only select among these four. First, this makes data entry faster.
Second, it avoids the possibility that someone will type in “asfault” instead of “asphalt.” The items
concrete, asphalt, macadam, and gravel constitute a domain for the roads feature. You could also set a
default value for roads. If no other value is entered, the value of the attribute would automatically be set
to “concrete.”
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