Geography Reference
In-Depth Information
101
TABLE 7-6
Shape_length
Highway_number
Lanes
831
4
101
4
171
2
FIGURE 7-12 Lines indicating roads
101,4,p
101,4,q
TABLE 7-7
Shape_length
Highway_number
Lanes Zone
171,2,p
831,4,p
831
4
r
831
4
p
171,2,r
171
2
p
171
2
r
831,4,r
171
2
s
171,2,s
101
4
p
101
4
q
FIGURE 7-13 Lines overlaid with feature class “A”
Suppose that we have three roads in the area of feature class “A.” See Figures 7-12 and Table 7-6. For
purposes of maintenance, we would like to know what zone each stretch of road falls into.
The overlay would produce a line feature class with seven lines as illustrated in Figures 7-13 and
Table 7-7. The Shape_lengths would be the lengths of the newly created lines.
Spatial Joins in General
The term “spatial join” has been coined to describe overlay and similar processes. Basically, spatial joins
share the idea of taking two or more spatial datasets, each with associated attribute tables, and creating
another dataset. Both the (geo)graphics and the attribute tables in the new set differ from those of the
originating datasets.
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