Structures for Storing Geographic Data - Introducing Geographic Information Systems with ArcGIS - page 279

8. Select the rule Point Must Be Covered By Line, since we want the water lines to go to
Fire_Hydrants. The third text field (Feature Class) should indicate Water_Lines. Now give
your attention to the right side of the window, where a cartoonish explanation of the rule is
displayed. Read what it says. Then, toggle the Show Errors check box to see which points
satisfy the rule and which don't. Points that turn red indicate points that don't obey the rule.
Click OK.
Validating Topology
9. Since we will only need the one rule, you may press Next after you examine the New Topology
window. Read through the Summary and, if correct, click Finish. You get a message that the
new topology has been created, and are asked if you want to validate it. Say Yes.
In this case validation means that the computer has looked at every point in the Fire_Hydrants
feature class to see if a line from Water_Lines comes to it, crosses it, or comes within 5 feet of
it. Those points that do not meet these criteria will be flagged as errors. For those cases where
the water line is within 5 feet but does not touch the hydrant, the water line will be moved so
that it does touch the hydrant.
10. Once validation is complete, the Hydrants dataset will contain an entry labeled Hydrants_
Topology. Click it in the T/C and preview its Geography. You should see two red squares. This
means that two fire hydrants were not within the cluster distance of a water line segment.
Let's use ArcMap so we can look at all three layers at once to see what's going on. See
Figure 4-25 for a preview of what you will see in ArcMap.
FIGURE 4-25