Exercise 4. Building a Base Map and a Point Coverage
CE 397 GIS in Water Resources
University of Texas at Austin
Goals of the Exercise
This exercise is intended for you to build a base map of geographic
and flow data for a watershed using the Guadalupe Basin in South Texas
as an example. This base map comprises watershed boundaries from the US
Geological Survey's Hydrologic Unit Code (HUC) coverage and streams from
the US Environmental Protection Agency's River Reach File 1 (RF1) coverage.
In addition, you will create a point coverage of stream gage sites by inputting
latitude and longitude values for the gages in a text file, creating the
coverage in geographic coordinates, and then projecting it into the same
projection as the HUC and RF1 files. You will then link to the US Geological
Survey's website in Texas, download some streamflow data and make a plot
of the flow hydrograph.
Computer and Data Requirements
This exercise uses both Arcview and Arc/Info. It should be executed
on the Dec Alpha workstations.
The HUC boundaries are a subdivision of the US made by the US Geological
Survey to show major and minor river basins. There are 2-, 4-, 6-, and
8-digit HUC boundaries, where the larger the number the smaller the area.
The HUC8 boundaries are the basic ones. I have selected from the maps covering
the whole United States, the HUC's and Rf1 reaches in the zone defined
by HUC2 = 11, 12 or 13 which is the region covering Texas and neigboring
States, and put them into coverages call Huctx and Rf1tx for you to work
on. The RF1 coverages have the names of the rivers and streams annotated
onto the stream arcs.
The HUC and RF1 coverages for the United States can be downloaded over
the internet:
USGS Hydrologic
unit code
EPA river reach
files
Procedure for the Assignment
Get Stream and Watershed Data for Texas
To start off, you'll copy the RF1 and HUC coverages from the GIS-Hydro
97 CD-ROM. Logon to a workstation and, at the $ prompt, make a directory
under your data directory called ex4:
$: mkdir ex4
$: cd ex4
Copy the files edwards.e00, huctx.e00, and rf1tx.e00 from
the directory gishyd97/class/base_map/gisfiles of the GIS-Hydro
97 CD-ROM to your working space. The files are in Arc/Info export format,
as indicated by the .e00 so you will need to import them using the
arc IMPORT command. Fire up Arc/Info using $arc, and then import
each of the coverages
Arc:import cover edwards edwards
Arc:import cover huctx huctx
Arc:import cover rf1tx rf1tx
Once these coverages are copied into your area, do a describe on each
of them and take a look at their projections. This information will be
valuable later because you will project gage locations into the same projected
coordinates.
Arc: describe huctx
Arc: describe rf1tx
Arc: describe edwards
Arc: quit
To be turned in: A copy of the description of the huctx coverage.
How many polygons are contained in this coverage? How many arcs are in
the coverage? What is the name of the map projection in which the data
are presented? What system was used to specify the projection parameters?
Selecting the Guadalupe Basin Watersheds
The Huctx and Rf1tx coverages cover a large region and we only want
to work in the Guadalupe Basin. We'll use Arcview to identify which HUC's
cover the Guadalupe Basin and to create new Arcview shapefiles of these
portions of the coverages.
Start up Arcview.
$: arcview &
Once Arcview is loaded, open a new view and add the huctx theme to your
view. Select (check mark) this theme in your view to get an idea of the
scope of this coverage. Recolor the theme as necessary. Highlight the theme
by clicking on its legend bar and use the table icon 
to bring up the table of its attributes. Scroll across the fields and see
the huc (8 digit huc's),huc2, huc4, huc6 items. With the Table window highlighted,select
the hammer icon 
. This
gets you into the Table Query Builder. Under "Fields", scroll
down to [Huc6] and double-click on it. Then click on the "="
sign. Finally, under "Values", scroll to 121002 and double-click
on it. You'll notice that your sequence has been recorded (in parentheses)
in Query Builder's scratch pad. Select New Set in Query Builder and you
can see the Guadalupe Basin highlighted in the View. Use the promote icon
in the Table window
to promote the selected records to the top of the table. You will see that
the Guadalupe Basin [huc6 = 121002]is comprised of four sub-basins, the
Upper [huc=12100201] , Middle [huc = 12100202] and Lower Guadalupe [huc
= 12100204]basins and the San Marcos basin [huc = 12100203]
.
Use Theme/Clear Selected Features to unselect the Guadalupe Basins in the
Table Query.
In order to avoid having to work with large data sets which take a long
time to draw on the screen, you are going to make a new theme containing
only the huc's in the Guadalupe Basin. To do this, highlight the huctx
theme in the legend bar, go to Theme/Properties, select the hammer icon,
open the Query Builder, build the [huc6] = 121002 query in the same manner
as you did previously, except that you select OK in both the Query Builder
and Theme Property windows to complete the selection. You'll see that now
only the Guadalupe River basin is displayed in the view.
Use Theme/Convert to Shapefile to produce a new theme. Name this theme
hucguad.shp and save it in your local workspace for this exercise. You
will be prompted to whether add this theme to the View. Do so, adding it
to View1 (not New View). If you click on the theme button for hucguad,
you'll see that it looks identical to the earlier huctx theme selection
for the Guadalupe basin. But the new hucguad shape file is much smaller.
A Shapefile is a special simplified file structure for storing geographic
features in Arcview. It can be converted to an Arc/Info coverage using
the Arc/Info command Shapearc if necessary.
Turn off the huctx and hucguad.shp themes in the View and Use the Add
themes button to select a new theme to add to the View. Select rf1tx. Click
this on and you will see a big display of the rivers of Texas and neighboring
states whose drainage comes into Texas.
Getting the Guadalupe River Reaches
Note that the same actions as you've just done in Arcview can also be
done in Arc/Info to build a new coverage which is a reduced copy of the
original coverage. Now, we're going to do the same thing in Arc/Info except
that we'll do it just for the HUC's in the Guadalupe Basin. Quit from Arcview
and start up Arc:
$ arc
[create a new coverage hucguadal from huctx according the criteria specified
in the following dialog]
Arc: reselect huctx hucguadal
Enter a logical expression:
: res huc6 = 121002
:
[hit return on this line to indicate that you have finished entering]
Do you wish to reenter this expression: (Y/N) N
[correct errors here]
Do you wish to enter another expression (Y/N) N
[add additional selections to make a more complex query if you want to
include or exclude other records (use asel to add records and nsel
to select the complementary set to the set previously selected)]
Now the reselection occurs and a new coverage hucguadal with just 4
HUC's is created (HUC =12100201, 12100202, 12100203, 12100204).
To get the corresponding river reaches, the Arc Intersect command is
used:
Arc: intersect rf1tx hucguadal rf1guad line
This should produce a line coverage of just the 94 arcs within the Guadalupe
Basin. I have been having some trouble running this function, and if it
doesn't work for you, import the rf1guad.e00 from the same anonymous
ftp site from which you obtained the other files for this exercise.
Quit Arc/Info, and start Arcview. Add Rf1guad as a theme to the View.
Highlight the huctx and rf1tx themes in the legend bar (use Shift when
highlighting the second theme) and the Edit/Delete Themes to delete them
from the Project. From now on, we'll work with the Rf1guad coverage and
the Hucguad Shapefiles to save time in displaying the themes.
Once you've got the Guadalupe Basin displayed, you can select the "Zoom
to extent of active themes" button 
to bring the Guadalupe Basin up to the full extent of the screen. Now you
should be able to see the Guadalupe River Basin with all of its major river
reaches. If you hit the "i" button with the huctx theme highlighted
and make an information query on one of the huc units, you'll see that
the last field in the attribute table is a "name" field.
Highlight the rf1guad theme, click on the table icon and bring up the
attribute table for this theme. Scroll across to the names of the rivers.
Pname is the name of the river segment and Cname is the name of the segment
to which this segment next connects downstream. Use the hammer icon in
the Table window to select [pname] = "Guadalupe R", and promote
the selected records to the top of the table. This shows the main channel
of the Guadalupe River. The small gap in the center of the basin is the
segment where the Guadalupe River flows through Canyon Lake, which is separately
identified in the Pname field.
After you've established this view, make a layout of the view and print
it. Save Project and exit from Arcview.
To be turned in: the layout of the Guadalupe Basin streams and watersheds..
Creating a Point Coverage of Stream Gages
Now you are going to build a new coverage yourself of stream gage locations
on the Guadalupe. I have extracted information from the USGS stream gage
data books information about 7 gages on the main stem of the Guadalupe
River (there are many other stream gages in this basin):
Seq# Station# Name Longitude Latitude Mean Annual
Flow (cfs)
1 08176500 Victoria 97 00 46 W 28 47 34 N 2095
2 08175800 Cuero 97 19 16 W 29 03 57 N 2094
3 08168500 New_Braunfels 98 06 35 W 29 42 53 N 552
4 08167800 Sattler 98 10 47 W 29 51 32 N 464
5 08167000 Comfort 98 53 33 W 29 58 10 N 215
6 08166200 Kerrville 99 09 47 W 30 03 11 N 186
7 08165500 Hunt 99 19 17 W 30 04 11 N 81
The flow data for each of the gages was obtained from the USGS Water-Data
Report TX-92-3.
(a) Define a file containing an ID and the long, lat coords of the
gages
The coordinate data is in geographic degrees, minutes, & seconds.
These values need to be converted to digital degrees, so go ahead and perform
that computation for the 7 lon/lat pairs. This is something that you will
need to do before going to the computer lab and it has to be done carefully
because any errors in conversions will result in the stations lying well
away from the Guadalupe River. I suggest that you prepare a table showing
the gage long and lat in degrees, minutes and seconds, convert it to long,
lat in decimal degrees using the formula
Decimal Degrees (DD) = Degrees + Min/60 + Seconds/3600
Remember that West Longitude is negative in decimal degrees.
Open Text Editor and create a raw data file that includes a gage
sequence # (i.e. 1, 2, 3, 4,...) and the longitude & latitude coordinates
converted to digital degrees. Note that longitude comes first and then
latitude (because this corresponds to (x,y) coordinates in a Cartesian
system).
Example: (this table should contain 7 records, the first one
as shown and the other six created similarly by you from the information
given above for each gage with the longitude and latitude typed into your
file to replace the ... entries given in the table below).
1 -97.012778 28.792778
2 ... ...
3 ... ...
4 ... ...
5 ... ...
6 ... ...
7 ... ...
end
DON'T FORGET TO TYPE 'end' (and press return) as the last line
of your data to signal to Arc later that this is the end of the stations
that you wish to enter.
Save this Text Editor file as lonlat.dat. If it saves to your
root directory, you can move it to your working directory where it is needed
by using from the working directory the Unix command
$ mv ~/lonlat.dat ./ [where ~ means "my root directory"]
You can also use the File Manager (file drawer icon on Dec tool bar)
to move files. Open two File Managers and use drag and drop to move files
from one location to another.
(b) Generate a point coverage showing the gage locations
Start up Arc, and then:
Arc: generate stations (this command invokes the "generate"
function to create a coverage called "stations")
Generate: input lonlat.dat (use the Text Editor file lonlat.dat
to define the data in your coverage)
Generate: points (this specifies a point coverage)
Creating points with coordinates loaded from lonlat.dat
Generate: quit
Externalling BND and TIC...
Arc: build stations points (with this command you actually create
the point coverage)
Building points...
Arc: addxy stations [adds long and lat as attributes X-Coord and
Y-Coord]
Arc: list stations.pat
Record AREA PERIMETER STATIONS# STATIONS-ID X-COORD Y-COORD
1 0.000 0.000 1 1 -97.013 28.793
2 0.000 0.000 2 2 ... ...
3 0.000 0.000 3 3 ... ...
4 0.000 0.000 4 4 ... ...
5 0.000 0.000 5 5 ... ...
6 0.000 0.000 6 6 ... ...
7 0.000 0.000 7 7 ... ...
Now you have a coverage with no attribute data in it. You'll notice
that the four default parameters are included for each of your records.
You should have 7 records because that is the number of coordinate pairs
in your lonlat.dat file.
Projecting the Point Coverage
In order to successfully overlay this point coverage on top of the RF1
and HUC coverages, it needs to be in the same projection as the others.
The point coverage "stations" has still not been defined as a
projection, but since the lon/lat values are in decimal degrees, that represents
geographic coordinates. We are going to do this using a projection file
which contains all the parameters that the project command will need.
Open a new Text Editor window from the Dec tool bar. Type the
following information into the file. The first part from "input"
to "parameters" tells the project command that the input coverage
is in geographic coordinates. The second part from "output" to
end specifies what the output coverage should look like. In this case the
projection also accomplishes a datum shift from NAD27 (the datum used for
USGS maps from which the latitude and longitude of gages was originally
extracted) and NAD83 (the current standard earth datum).
input
projection geographic
datum NAD27
units dd
parameters
output
projection albers
datum NAD83
units meters
parameters
27 25 00
34 55 00
-100 00 00
31 10 00
1000000.0
1000000.0
end
Again, be sure to hit Return after you type end. Save the file and call
it albprj. If necessary, move it to your working subdirectory using
$mv ~/albprj ./
You can also use the File Manager (file drawer icon on Dec tool bar)
to move files. Open two File Managers and use drag and drop to move files
from one location to another.
Keep this file albprj for use in later exercises as it saves having
to remember all the details of what is needed to do a projection. A small
library of similar projection files is contained in the directory /res2/maidment/proj/
that you may wish to use at a later time in your own project work. Making
and using projection files is a very important part of building data bases
because the data have to be assembled from various locations and projected
into the same geographic reference coordinates.
Arc: project cover stations albstat albprj (this command will
project the coverage "stations" into an albers projection called
"albstat" using the projection file "albprj")
If you get a projection dialog, i.e. Projection:, it means that
the albprj file could not be located or is not complete. Make sure that
the albprj file is in your current working directory.
Arc: list albstat.pat
Creates a listing of selected items from the point attribute table (pat)
of the new coverage.
Now do a describe to show the projection information which should be
compatible with huctx, rf1tx, and edwards,so that they can be displayed
together:
Arc: describe stations
Arc: describe albstat
Arc: quit
To be turned in: a description of the coverages stations and albstats
which shows their projection parameters.
View and Add Attributes to the Point Coverage
Now fire up Arcview again:
$ arcview &
Open the view that you created in the first part of the exercise with
the Huc and Rf1 files on it and add the theme Albstats to it. The USGS
stations from your point coverage should fall exactly on the main stem
of the Guadalupe River. Pretty cool !!! This stuff really does work! Now
we are going to add the USGS gage Id,gage name, and annual discharge for
each gage as a new attribute in Arcview.
Creating a New Data Table Click on the Table icon in the Project
Window and Select New. You will see a blank table appear. In the Table
Window, Under Table, use Start Editing to initiate the editing of the new
table, then under Edit Add field to create a new field in the Table. In
the dialog box that comes up, type
name Number
type number
width 4
decimal places 0
You will see the new field called Number come up in the attribute table.
Continue adding fields as follows:
name USGSID
type string
width 12
name Name
type string
width 16
name Flow
type number
width 8
decimal places 0
Once you've done this, go to Table/Stop Editing to save the new fields.
If you make a mistake in adding the fields, use Table/Start Editing again
and Edit/Delete Field to get rid of the field that you wish to replace.
Add a replacement field. It always gets added to the right hand end of
the table but you can relocate it in the table by dragging its field name
to a new location. Use Table/Stop Editing to save the new table fields.
Adding Data to the Table
Use Table/Start Editing to begin adding data, then Edit/Add Record to
add a record to the table. Do this seven times to create space for the
data on the 7 gages. Now go to the icon bar on the top of the display and
select the I button with an arrow on it (just to the right of the I button
without an arrow on it).
Go down into the table and you'll see a little hand and finger appear.
Use this to click on the record whose value you want to fill in and add
the appropriate data value. Continue adding the data values until they
are all done.
The following data are needed in the table:
Number USGSID Name Flow
1 08176500 Victoria 2095
2 08175800 Cuero 2094
3 08168500 New_Braunfels 552
4 08167800 Sattler 464
5 08167000 Comfort 215
6 08166200 Kerrville 186
7 08165500 Hunt 81
Click on any depressed field labels you have to undepress them. Then
select Table/Stop Editing to close the table. Note that you can only edit
tables for which you have write permission (i.e. your own tables not tables
in my work area).
Joining the Data Table to the Point Attribute Table
Go to the Table icon in the Project Window again, and select Add. Choose
Attributes of Albstat.
Go to the Data table and depress the Number field label. Go to the Attributes
Table and depress the Albstat# field. The order in which you do this is
important. You should now have two tables appearing like this:
Notice how there is a one to one relationship between the values in
the Number field of the Data table and the Albstat# field of the Attributes
of Albstat table. This is the key field that will be used to join the two
tables together.
Use Table/Join to accomplish the Table connection. You will now have
an Attributes of Albstat table that looks like this:
Some of the attribute fields (shape, area, perimeter) have been omitted
from this view for clarity.
Labeling the Gages in the View
Now you can use the Name field that you've added as a label for the
gages in the View. Go to the View window and under Theme/Properties select
the Label symbol. You'll be prompted with a dialog box which permits you
to specify what item is to be used as a label. Scroll down to select the
Name field. Then use Theme/Auto Label to add the names to the view. You
can use Window/Show Tool Palette with the text option to change the size
of the labelings. You can use drag the labels around to get a more pleasing
arrangement provided the arrow button in the View toolbar is depressed.
You can now create a view like this:
Pretty awesome!
Creating a Chart and Layout
Create a chart of the mean annual flow of the Guadalupe gages by highlighting
the Attributes table, select Table/Chart in the pulldown menus, and in
the dialog box that appears, Add Flow to the display and label the fields
with Name. A bar chart will appear. To edit the title and axes of the chart,
use the small pen tool which is third from the right in the lower tool
bar in the Chart window and then click on the chart feature that you want
to alter.
Prepare a layout showing a map of the drainage area, the graph of its
annual flows at each gage and a table of numerical values describing the
gages. If you add a table or chart and it comes up blank, check that the
Display Always option is used and that the window that you have opened
in the layout is large enough to display the object that is to appear in
it. If necessary resize the original chart or table smaller so that it
can be displayed in the layout. You'll see in the chart that the flow in
the Guadalupe River at Cuero and Victoria is much higher than in the upstream
stations. That is because the flow from the San Marcos river joins the
Guadalupe upstream of Cuero.
To be turned in: a layout showing the base map, chart and data table
for the Guadalupe River flows
Overlaying the Edwards Aquifer
The Edwards aquifer is one of the most critical water resources of Central
Texas. It is the main source of water supply for San Antonio, the 10th
largest city in the United States. The Edwards aquifer is recharged by
infiltration from rivers crossing its outcrop area. To determine where
the Guadalupe river crosses, the outcrop area, I obtained a coverage of
the Edwards aquifer from the Texas
Natural Resource Information System by selecting through the menu system:
GIS/hydro_geology/major_aqu_e00 where the file edwards.e00 is found. I
downloaded this file by logging in to TNRIS using anonymous ftp to: www.twdb.state.tx.us
and changing directories to pub/GIS/hydro_geology/major_aqu_e00. Use binary
in ftp before downloading files from this area. It seems that you should
be able to download this from Netscape but the file displayed on the screen
when I did this so I used anonymous ftp to get it directly.
The edwards aquifer coverage from TNRIS is in standard Texas State Mapping
System coordinates which are presented in a Lambert Conformal Conic projection.
We are using the same coordinates but in an Albers projection because it
preserves earth area. I projected the edwards coverage from Lambert to
Albers TSMS coordinates using the prj file Lambtsms.prj in the projection
library in /res2/maidment/proj. This is the coverage Edwards that
you copied from my directory at the beginning of the exercise.
Add the Edwards theme to your Guadalupe project. Click on its legend
and label the theme using the attribute Aquifer. This attribute has three
values: 1 for outcrop, 2 for downdip and 0 for holes within the outer boundary
of the aquifer. Classify the values with Unique Value and color them appropriately.
You'll see that the Guadalupe river flows South East towards the Gulf Coast
and it cross first the outcrop and then the downdip portions of the Edwards
aquifer. The downdip region is where the aquifer dips below the land surface
and is shielded from the surface rivers by overlying hydrogeological units
of low permeability. The Edwards is a fissured limestone aquifer whose
fissures lie along its Southwest to Northeast orientation, so its flow
moves in that direction, transverse to the direction of flow in the Guadalupe
basin. It is thus quite possible for water to drain from the Guadalupe
river into the Edwards aquifer and then reappear as a spring further North
in another river, such as Comal springs feeding the Comal river. Zoom in
to the region where the aquifer crosses the Guadalupe basin for a closer
look.
To be turned in: Between which two gaging stations does the Edwards
aquifer outcrop area occur? What is the difference in mean annual flow
at these two gages? Comment on these data. Do they seem correct to you?
Downloading USGS Flow Data
There are also other sources of flow data. One of them is via Internet
from the U.S. Geological Survey
in Texas. To retrieve stream flow data from that site go to the Online
Hydrologic Data and then to the Texas Surface-water Database
section. You'll see several scroll down windows which allow you to find
your stations(s) by Basin, USGS HUC, County, station type or station name
or number. Select the Guadalupe River Basin and Station Type Surface
Waterhit "Find stations". There 99 surface water stations
in the basin. Select the stations for this exercise by clicking on them.
I chose the Guadalupe River at Victoria. Then click on "Get retrieval
form for the selected station(s)" You now have to specify what data
you want to retrieve. Select to retrieve "DISCHARGE, IN CFS FROM THE
DCP" from each station, and (near the bottom of the page) specify
the time interval(I selected 1/1/91 to 12/31/93 because there was a large
flood in South Texas in Christmas of 1992 and I wanted to look at its flow
characterstics. It is clear that the first six months of 1992 were a very
wet period when compared to the corresponding periods in 1991 and 1993.
Select "Return graph". Then click on the "Make data retrieval"
button (Retrieving the graph may take awhile). Pretty cool! You can also
download data from this source or create graphs for different time periods.
You'll eventually get a plot of Discharge vs. time for your selected station.
My graph looks like this:
Print your graph from Netscape.
To be turned in: a graph of the discharge from one of the USGS stations
on the Guadalupe River.
Cleaning Up
When you're done with this part of the exercise, you'll need to clean
up:
$Arc
Arc: kill stations all
Arc: kill albstat all
Arc: kill huctx all
Arc: kill rf1tx all
Arc: kill hucguadal all
Arc: kill rf1guad all
Arc: kill edwards all
Arc: quit
$: rm data.dat
$: rm lonlat.dat
$: rm rf1guad.* [removes several files]
$: rm hucguad.* [removes several files]
Keep your projection file albstat.prj around for future reference. Remove
any other files and directories from the working directory using the rm
and rmdir commands. If you want to remove all the files underneath a particular
directory and also the directory itself, use
rm -R directoryname
but be very careful when you do this because it will silently kill
off everything under directoryname! More efficient than James Bond!
Ok! You're done!
These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources,
The University of Texas at Austin. All commercial rights reserved. Copyright
1997 Center for Research in Water Resources.
.
