Manual modification of shapefiles September 19, 2002
Lab#1 Editing basins with the split polygon tool
General lab objectives: find lab in lab02 /basins/modify/mod1
Find basin candidates for repair or division.
Correct a basin error using the split polygon tool.
Divide a basin using the split polygon tool.
Add a new basin using the split polygon tool.
Specific lab objectives:
Identify candidate basins for splitting based on basin area.
Identify candidate basins for repair at the intersection of HUC boundaries or
stream intersections with major rivers or lakes.
Correct the mouth of the Chartiers Creek watershed (ffmp_id 1446) using split
polygon tool.
Divide the Chartiers Creek watershed (ffmp_id 1446) using split polygon tool.
Add the Whiskey Run watershed (in ffmp_id 1446) using split polygon tool.
Lab Instructions: “Looking for trouble in all the right places”
Open the county warning area view.
Make the basins theme active
Find candidate basins for splitting based on area
Click on the query button.
Do a query ( [Cwa] = “PBZ” and ( [Area_sq_mi] >= 10.0)
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Select “new” set.
Click on the table button
Click on the promote button
for basins to see selected watersheds.
to move them to the top of the list.
All basins in your CWA with areas greater than 10 mi2 are prime candidates for
splitting. You may want to consider splitting urban basins greater than 5 mi2.
Find merger of HUC’s to check for delineation errors
Because HUC’s were merged by NSSL to create the basin file, check for
possible errors at the intersection of two or more HUCs.
How do I find a HUC?
Turn on the basins.shp theme and make this theme active
click on “clear selected features” button.
To find a HUC using the Pfafstetter do the following query.
Click the query button
(include quotation marks for Pfaf_id!!!)
( [Pfaf_id]>=”1466000000000”) and ([Pfaf_id]<=”1466999999999”)
(nine-zeroes)
(nine-nines)
Select “new” set.
This query will select all aggregated basins found in HUC 05010009 since all
defined basins in this HUC begin with the number 1466.
Click on “zoom to selected feature” button.
An alternate way to find HUCs is to display EPA RF3 files
Turn on the Allegheny River theme. This file is the EPA RF3 file for HUC
05010009. The few streams that fall outside the selected HUC are errors in the
EFP RF3 file.
Turn off the basins theme and turn on the A_basins theme and make it active.
Click on the “zoom to active theme” button.
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Turn on the theme for the Monongahela River (HUC 05020005), the
Youghiogheny River (HUC 05020006), and the Ohio River (HUC 05030101).
Turn on the identify button
sample some basins in each HUC.
Recall that the first 4 digits of the Pfafstetter ID should be the same for all basins
in a HUC. Four different HUCS intersect in Allegheny County:
Allegheny River 1466, Monongahela River 1471, Ohio River 1473, and
Youghiogheny River 1472.
Turn on the Dpoint theme and make the Dpoint active.
Click on the “zoom to active theme” button.
Turn on the ffmpnum theme.
Identify
the last downstream basin of the Allegheny River (ffmp 1520), and
the Monongahela River (ffmp 3796) to see if the first 4 Pfaf digits and the stream
names are correct.
FFMP 3796 is correctly named Monongahela River, but FFMP 1520 is incorrectly
named Ohio River instead of Allegheny River.
Turn on the national hydrologic data set of streams (A_nhd) and notice the major
rivers are a single line in the center of the river channel. Now turn on the NSSL
derived stream (A_streams) and notice they tend to run along the river bank. The
long pipe artifact of 1520 and the extension of 3796 into the Ohio River result
from the intersection of the NSSL derived river reach about 0.8 miles too far
downstream.
Editing Chartiers Creek using the “split polygon” drawing tool
Turn on the Chartiers Creek view.
Turn on the “char” theme to highlight the boundary of FFMP #1446
Look for delineation errors where streams flow into wide rivers
Turn on the “extra” theme and the “9781” theme.
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The radar bins in “extra” and “9781” do not belong in Chartiers Creek ffmp
segment 1446. Use the “split polygon” drawing tool
to remove them.
Turn on the char0 theme as a guide for drawing the line.
Make the A_basin theme active.
In the theme menu select “start editing”.
The “split polygon tool”
is cleverly hidden in the pull down menu for the
drawing tools.
The line to split the polygon must start and end outside the polygon to be
split.
After the split is complete, in the theme menu select “stop editing” and then say
“yes” to save edits. Look at the table
of the two split segments.
The area chopped off of Chartiers Creek should be part of the Ohio River
segment ffmp# 1519.
Merge the split segment of Chartiers Creek with FFMP# 1519.
With A_basins active start editing.
Use the select tool
to select one of the segments. Black squares will
surround the selected shape. Hold the shift key down and select the second
area to be merged.
In the edit menu select “union features”
Stop editing
Save edits.
(Warning:: If you use Combine features
all attributes will be reset to zero or
blanks)
Use the identify button and check the attribute table of the newly defined Ohio
River segment.
If you could maintain the attributes of the old Ohio River segment 1519, no
manual attribute editing would be necessary since the Pfafstetter numbers do not
need to be changed and the names also remain the same. Only the
recomputation of area would have to be accomplished.
Divide the Chartiers Creek watershed (FFMP 1446) into three segments using
the split polygon tool.
Use the char1 and char2 themes as a guideline to
draw the lines with the split polygon tool.
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Edit the table entrees for the newly created segment to modify the Pfafstetter
number. FFMP_id numbers are generated during AWIPS localization process, so
the FFMP_id can not be manually edited. Edit the stream name to read
Chartiers Cr(1), Chartiers Cr(2) for the two newly created basin segments.
Add Whiskey Run as a new watershed.
The small tributary in the southern portion of the Chartiers Creek (FFMP 1446) is
Whiskey Run. Use the split polygon tool
to define a basin for Whiskey Run.
Use the char3 theme as a guide for drawing the line.
After you stop editing and save edits, edit the attribute table to change the
Pfafstetter ID and the stream name for the whiskey run segment.
End of lab#1.
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