Geography Reference
In-Depth Information
25. Right-click on the field name Seg_Len and click Field Calculator. Ignore any warning.
The segment length can be calculated by subtracting the beginning mile point from the ending
mile point.
26. Calculate Seg_Len as [END_MP] - [BEGIN_MP]. The calculation will take place only for selected
records. Click OK. By looking at the table, verify that Seg_Len does indeed contain the positive
difference between the beginning and ending points.
27. Run Statistics on Seg_Len. What is the Sum? ________. Divide the length of the route in
feet that you found previously by the number of feet in a mile (5280). The result should be
reassuring. ________.
28. Using Table Options > Select By Attributes (Method: Select From The Current Selection), obtain
those segments of 30000030 that have RATING >75. How many miles are in these segments?
_______.
29. Since you know the total length of 30000030 >75 you can easily calculate the total of the
segments that are <= 75. How many miles? ________.
The intersection of point events and line events has a lot in common with its polygonal counterpart.
The graphic result will consist of those points and segments that occupy common space. The resulting
attribute table will reflect both event tables. We will do an intersection operation for all route segments
and all accident event points. (There are certainly more efficient ways to do this, as far as number of
calculations is concerned, but this is the most straightforward.)
The process will be to intersect the accident and pavement event layers for the entire region to produce
a new event table, consisting of records of pavement event segments where the segments contain
accidents. This table will then be made into a (temporary) event layer and displayed. From that we will
select those with ROUTE1 value 30000030.
30. Display All Records of Pavement Events. Clear Selected Records. Close that table. Show
ArcToolbox. In Linear Referencing Tools, right-click on Overlay Route Events and select Open.
31. In the Overlay Route Events window, click the down arrow at the end of the Input Event text box.
Select Pavement Events. The next four text boxes should be filled in for you. For the Overlay
Event table, pick Accident Events in the same way as Pavement Events.
32. Browse for where to put the Output Event Table to
___IGIS-Arc\ YourInitials\ Linear_Referencing
and call it Accidents_and_Pavement.dbf. Accept the rest of the form. Click OK. You may have to
wait a bit, since thousands of point events are being matched up with hundreds of segments.
What you have now is a table named Accidents_and_Pavement.dbf. Open it and explore it. As with most
output from overlay operations there are lots of fields (from each of the contributing feature classes) and
lots of records. To see the graphics, you must make a layer, using a tool in ArcToolbox.
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